Ive used bitcoin for a while and I know how to send/recieve etc I thought I was reasonably understanding of them but I have recently stated using a blockchain.info wallet.

In the app that comes with it on my phone there is a message that says sharing your xpub key enables others to disrupt your transations. I cant get my head around what this apub is and how it differs from when i just go onto the site and log in, press recieve and get a number to request btc to be sent to.

Can anyone point me in the right direction, i am wondering if I have been doing something wrong or if the blockchain app words differently to the other wallets I have been using