Glossary
Full buy
In one line: A round where the whole team buys main weapons, heavy armor and abilities.
What it means
A full buy means buying everything: a rifle (or Operator), heavy armor and every ability you need. It is when the team is at its strongest, and the whole point of managing the economy is to have as many full-buy rounds as possible.
A full buy makes sense when everyone can do it. If a teammate is short, whoever has plenty can buy them a gun (a "drop"). Five players with rifles beat four with Operators and one with a pistol.
An example
In round four after an eco you all have over 4000 credits. You buy Vandals or Phantoms, heavy armor and your abilities. You have 6000, so you also buy a rifle for the teammate who only has 3000.