I'm going to attach three pages from the NazaM manual.
It's where many users are first introduced to IOC.
IOC is pretty well explained there.
As one progresses with DJI FCs and airframes, the explanation becomes less detailed because it's assumed that you are already familiar.
I'm also attaching the IOC explanation page from the I1 manual...
Not sure if you are familiar with these 2 modes,but here is a link about it.It's Spanish ,but very clear about Home lock and Course lock.And it's about the Phantom,but pretty much the same on the Inspire.