Whatsapp - last time seen online - what does it mean?

I'm using whatsapp and some of my contacts have been seen online AFTER my messages have been delivered..

My question is: If I read something like this:

[10:01] my message is delivered The contact has been seen online at 10:08

Does this mean the contact has read my message/opened whatsapp by himself? Or does it mean that his Android OS has let Whatsapp application

Answer

Just to bring this current, WhatsApp have updated their What are those check marks next to my messages? page to highlight that there's a new feature to see when a message is actually read.

Check marks will appear next to each message you send. Here is what each one indicates:

message successfully sent.

message successfully delivered to the recipient's phone.

the recipient has read your message.

It's still likely that a message will show as delivered before a user has been "online" to actually read it.