Floor Joist Wood Rot
This is the area located underneath a bathtub that was installed
correctly, but the bathtub surround wasn't. I honestly couldn't believe what
I was looking, when we removed the exterior stucco and found extensive wall
framing damage that eventually led to this.
Damaged floor joists will need to be replaced and this isn't always going to be easy. Something like this can require structurally supporting sections of the building and might require someone with extensive knowledge about house framing and repairs.
What you're looking at here is a floor joist suffering from dry rot, not termite damage. If you're planning on doing your own home inspections, you will need to know the difference.