Data is content sent across the internet. Any time you upload (send) or download (receive) a text, picture, video, or application, or look at a website, you are using data. 

Whenever you use the internet on your phone, you are using ‘data’. This means you’ll need to buy data from your mobile network provider. Some activities on the internet use more data, so cost more to do.” “You can buy data for the internet; it is like buying phone credit for calls and messages. Data for the internet can be bought from your local mobile network agent or phone credit seller who will top it up for you.” “Sometimes internet data can also be bought in ‘data vouchers’ or ‘data cards’ that you can use to top up your mobile internet yourself.