Homolog/ortholog

[Yamagata 山形]

How do you define a homolog, ortholog, or paralog?  Family, superfamily,
subfamily, cognate, counterpart, related, homologous, --Do you use other
words for describing relationships among homologous genes?  And, how would
you use these words?  Is there good references for how we can accurately
distinguish these words?  I know there is no simple answer for this.  But,
I would like to know how molecular evolutionalists are using these words. 
Thanks in advance.