A strategy is a combination of compute + schedule which can be used to implement an operation efficiently. For example, for conv2d we register both a regular conv2d compute + schedule and a winograd conv2d compute + schedule as appropriate.
When autotuning, the list of strategies for an operation will then define our search space (e.g. we will search both winograd and regular conv2d implementations for conv2d).
I think the remaining confusion might be about the difference between compute and schedule. I am not an expert on this but they are similar to Halide compute and schedules. Take what I say as a grain of salt. The compute is a more declarative math expression which naively can be lowered into a set of for loops. The schedule is then a transformation of this naive set of for loops to add things like tiling, transposing axes, etc. It’s enumerations are what actually define the search space for that strategy in autotuning. However this schedule of course will only make sense for the compute it was designed for.