On whatsapp for iphone, what does the date to the right of each contact in 'chats' mean?

[iMore Question]

Next to a contact in 'chats' it says yesterday. Does that mean this contact was messaged or messaged me yesterday or would it also say yesterday if I had deleted the conversation yesterday?

 

[bones467]

That is the last time that "chat" had any activity, from anyone in the group.