What is base allocation?
Base allocation is the process of assigning bases to pilots or cabin crew. The base is the place a pilot is going to fly from.
In general, there are two types of airlines regarding the base system. The first are hub airlines which usually have only one base. For example, Emirates and its Dubai base. Then there are point-to-point airlines with a network of bases, for example Ryanair or easyJet.
This means that working for Emirates you will always be flying from Dubai (with possible overnights in destinations), but working for a point-to-point airline means you can be assigned any base in the network to fly from.
Pilots are usually based in one place for an extended period of time, unless they have a floating contract (see floater pilot / mobile pilot).
You should consider this when applying for an airline job as a pilot. You may be allocated to a base away from your home, which means relocation for you and possibly your family.