It is important to understand that "Focus Lock" is a general term that can be used to describe a number of different shooting techniques. Indeed, the goal of most photographs is to "lock focus" on a subject, and this can be achieved in a number of different ways.

Some photographers use this method described above, which is, autofocusing in Single/One-Shot focus mode, by half-pressing the shutter release button, and using the Focus Lock (AF-L) button when necessary. This is different than actively "locking" autofocus off by switching from autofocus to manual focus entirely, but the objective is the same, and which method you choose will be based on the activity of your subject.