Acronym Term Definition
ABC Amended birth certificate The birth certificate issued with the adoptive parents names. Some states allow access to both ABC and OBC.
atDNA or aDNA Autosomal DNA Autosomal DNA is a term used in genetic genealogy to describe DNA which is inherited from the all 22 chromosomes and from both parents. Autosomal DNA tests are available through FamilyTreeDNA.com, 23andMe.com and Ancestry.com.
BP Base Pairs Base pairs are used as a measurement of the size of an individual gene or an organism’s entire genome. In molecular biology, two nucleotides on opposite complementary DNA strands that are connected via hydrogen bonds are called a base pair. In DNA base pairing, adenine (A) forms a base pair with thymine (T) and guanine (G) forms a base pair with cytosine(C). The number of total base pairs is equal to the number of nucleotides in one of the strands. The human genome (23 chromosomes) is estimated to be about 3 billion base pairs long.  A kilobase (kb) is a unit of length in molecular biology equal to 1,000 base pairs of DNA or RNA. A Mega base pair = 1,000,000 bp.
CI Confidential Intermediary Usually a court appointed search professional that is allowed access to sealed records in order to find another person in the adoption triad
cMs Centimorgans A centiMorgan (cM) is a measurement of how likely a segment of DNA is to recombine from one generation to the next. A single centiMorgan is considered equivalent to a 1% (1/100) chance that a segment of DNA will crossover or recombine within one generation.  For humans  one million base pairs (bp) average about one centiMorgan. However the rate of recombination is highly variable.
DNA Deoxyribonucleic Acid DNA is found in every cell in your body except the mature red blood cells. It is located in a part of the cell called the nucleus. DNA contains all the information necessary to create your body and help it to coordinate the functions of your body from wiggling your toes to operating your heart. Some of your DNA also has information on your genetic heritage. The three types of DNA that are used in genealogy are autosomal, mtDNA and Y-chromosomal
FF Family Finder Family Finder autosomal DNA test from Family Tree DNA
HG Haplogroup Your haplotype is your unique DNA profile. It is determined by examining the variations (alleles) present at certain short tandem repeated (STR) loci and can be used to disprove relatedness to others  or establish that they may be related if their test results indicate their haplotype is the same or very similar to your own (we refer to these as matches). Others with haplotypes similar to yours will be in your haplogroup a geographically based collection of individuals with genetic similarities.
IBD Identical By Descent This means the DNA matches because it comes from a common ancestor. IBD can refer to a single mutation or to a segment of DNA. If a mutation or segment of DNA is IBD among a group of people it comes from a common ancestor.  The Family Finder relationship predictions require a minimum number of results in a row to be identical in order to identify that the segment is likely to be IBD. Refer to this article for more information about IBD vs. IBS.
IBS Identical By State Meaning the DNA matches by coincidence. When two individuals share numerous individual results without being related  those results are IBS. It also can happen when a very small segment from your mother aligns with a small segment from your father and the computer reads it as a match with some other person. These are also known as “False positives”.
ICW In Common With When two matches are ICW with each other.  This can then be used to triangulate your match (find their common ancestor which is likely your common ancestor too IF the two ICWs also match each other). For definiftion of triangulation see: http://www.isogg.org/wiki/Triangulation
LDA Late Discovery Adoptee Someone that discovers that they are adopted later in life
LNU or MNU Last Name Unknown or Maiden Name Unknown Used on trees to indicate that the surname or maiden name is unknown.
MRCA Most Recent Common Ancestor The most recent common ancestor is the first or closest ancestor you share with a DNA match or relative. All the ancestors of your MRCA are known as Common Ancestors because they are further back in time or less recent.
mtDNA Mitochondrial DNA The genetic material found in mitochondria. It is passed down from females to both sons and daughters but sons do not pass down their mother’s mtDNA to their children.
NFD No Further Details No additional information available.
NIST National Institute of Standards and Technology The National Institute of Standards and Technology is a non-regulatory government agency which sets the industry standard for DNA tests. FTDNA, 23andMe and Ancestry.com adheres to these standards in their DNA products and services.
NME Non Maternal Event Mother on paper is not the biological mother. Happens when a mother dies the father remarries and his second wife is the assumed mother.
NPE Non Paternal Event Father on paper is not the biological father or the child takes the mother’s surname and the father is typically unknown to future generations
OBC Original Birth Certificate Birth Certificate issued with names of biological parent(s) listed. In some states this document is sealed forever but in others it is available for a small fee.
OLS Overlapping Segment In autosomal DNA analysis when two people have the same or close to the same amount of DNA on a single chromosome.
rCRS or CRS Revised Cambridge Reference Sequence The revised Cambridge Reference Sequence (rCRS) is the reference standard against which all mtDNA sequences are compared. Having no differences from the rCRS is just as useful as having multiple differences. If the CRS had been created using a person of African or Asian descent then your observable differences would be different. Having no differences from the rCRS helps narrow down maternal lineages and haplogroups.
RF Relative Finder the autosomal DNA test offered at 23andME
SNP Single-Nucleotide Polymorphism A single-nucleotide polymorphism is a DNA sequence variation occurring when a single nucleotide  A  C or G  in the genome (or other shared sequence) differs between members of a biological species or paired chromosomes in a human
STR Short Tandem Repeat A short DNA motif (pattern) repeated in tandem. ATGC repeated eleven times would give the marker a value or allele of 11.
SDX Soundex Soundex is a phonetic algorithm for indexing names by sound as pronounced in English. The goal is for homophones to be encoded to the same representation so that they can be matched despite minor differences in spelling. The algorithm mainly encodes consonants; a vowel will not be encoded unless it is the first letter.