Buffer 🆚 Leeway

Leeway and buffer are two different concepts with distinct meanings.

Leeway refers to the amount of flexibility or wiggle room that is allowed within a particular situation. For example, you might have a couple of good solutions each of which could work and you have been given a green light by your client to choose by yourself based on the situation.
Buffer, on the other hand, refers to something that is used as a cushion or protection against potential problems or risks. For example, you might build in a buffer of extra time to a project schedule to account for delays that might occur, i.e. plan ahead to give yourself more time.

In short: leeway is about flexibility, while buffer is about protection.
Buffer is an extra amount of sth (money/time/resources) that you have.
Leeway - is freedom of action available to you in a certain situation.

Having a buffer gives you leeway.

A buffer gives project managers a leeway when unforeseen events occur and is often associated with scheduling in project management. A buffer can be temporal, financial or qualitative in nature, i.e. you have additional time, money or people available for difficult project phases. Buffers can be assigned either to the whole project or to individual activities.

Time buffers (also called lags or slacks) are often used in combination with time constraints in the project to create some flexibility. Activities that you must complete on time and can't have any delays are displayed on the critical path in the project plan (e.g. in a Gantt chart or network diagram).