What does online on Whatsapp mean?

I keep talking to a friend on Whatsapp, I text her when she is online. 90% of the time she doesn't answer but eventually, when she does she says that she doesn't check whatsapp that often and claims that she didn't see my message.

I wanna know if it is possible that this is true.

P.S. I'm using iPhone 4s and she uses Samsung Galaxy S3 if this helps.

The Online on Whatsapp means that the person is online and can see your message but i guess she don't want to reply to you. You can also check the same by checking the double green right click sign. This means that your message is being delivered to the recipient.

She needs to login everytime to check the messages and so, may be she is telling truth.