What is zest?
The zest of a citrus fruit is the orange, yellow (lemon) or green (lime) part of the outside of the fruit. Once you get to the white part (pith), this is no longer desired.
The zest is full of the rich flavours of the fruit, the pith is bitter.
If you are asked to zest a citrus fruit, you are either asked to grate, peel or shred. If you are grating, just grate the very outer part. If you are peeling or shredding use a knife or peeler, being careful to remove as little of the pith as possible.