ICA is an abbreviation for "Independent Computing Architecture"
Its defined by Citrix as:
"... the foundation of
Citrix server-based computing with MetaFrame XP and ICA
Client software. In simplified terms, the ICA
protocol transports an application's screens from a MetaFrame XP
server to ICA client users, and returns the users' input to the application server."
And in my simplified terms - its basically a fancy version of Microsoft's
Remote Desktop Protocol (RDP).