In genetics, to identify the locations and the coding regions of genes in a genome and determine what those genes do. To annotate (irrespective of the context) is to add a note by way of explanation or commentary. Once a genome is sequenced, it needs to be annotated to make sense of it.

1733, from Latin annotatus, past participle of annotare "to note down" (see annotation). Related: Annotated; annotating. Not in Johnson's "Dictionary," but used therein in def [..]

to make notes on, comment

v. To make explanatory or critical notes on or upon.

tat·ed -tat·ing vi : to make or write an annotation vt : to make or write annotations for an·no·ta·tor [-tā-tər] n

make notes on the script about performance details such as interpretations, motivations, moves, blocking and intonation patterns.

(v) add explanatory notes to or supply with critical comments(v) provide interlinear explanations for words or phrases

1. <computer programming, compiler> Extra information associated with a particular point in a document or program. Annotations may be added either by a compiler or by the programmer. They are not usually essential to the correct function of the program but give hints to improve performance. 2. <hypertext> A new commentary node linked to [..]