FASTA Format
Description line starting by '>' followed by name and then description;
Sequence in standard IUB/IUPAC amino acid and nucleic acid codes 
starting on the next line until description line of next sequence or 
end of file is reached. '-' often represents a gap of indeterminated 
length.

Example:
>albumin of human origin 
MKWVTFISLLFLFSSAYSRGVFRRDAHKSEVAHRFKDLGEENFKALVLIAFAQYLQQCPFEDHVKLVNEV
TEFAKTCVADESAENCDKSLHTLFGDKLCTVATLRETYGEMADCCAKQEPERNECFLQHKDDNPNLPRLV  
RPEVDVMCTAFHDNEETFLKKYLYEIARRHPYFYAPELLFFAKRYKAAFTECCQAADKAACLLPKLDELR  
[...]

The description line (or header line) is often used to add information,
but there is no formal definition; here just to mention a few usages:
>name
>name description
>name accession description
>namespace|accession.version|name description
>gi|identifier|namespace|accession.version|name description (NCBI)

Example:
>gi|412163|emb|CAA00606.1| albumin [Homo sapiens]