correct use of homology-identity-similarity ?

[Carsten Hohoff]

Where can I find the definition of 'homology', 'similarity' and 'identity'
in sequence alignments ?

We just had a discussion in the lab about this topic - I thought, 'identical' 
amino acid means the same aa, while  'similar' means a related (e.g., basic, 
acid, hydrophobic etc.) and 'homolog' is just a rough description of a
relationship based on sequence alignment...


Any hints that could help clarifying these terms are highly appreciated

Best regards


Carsten Hohoff