Jack:
Android is the operating system which the vast majority of smartphones and tablets run on.
In 2013 Tesco entered the market for tablets with their own device, called 'Hudl' (with the updated 'Hudl 2' swiftly following on). It used a modified version of Android. It was extremely popular and very well-reviewed but it can't have made much money for Tesco as they withdrew it from sale in October 2015.
For price alone, the closest equivalent is now the Amazon Fire range of tablets. They use a heavily-customised version of Android, meaning that there's not full access to all of the apps that can run under 'proper' Android. (Amazon try to tie users in to using things which they can make money from).