Yes, corrosion. Of course there will be some surface rust underneath - it's knowing when it is more than just that.
Check the MOT history of course, it gives a good understanding of how the car has been looked after, as well as any actual issues needing to be resolved.
See if there is some evidence of cam belt/water pump being changed - every 5 years is the max really (4 recommended) - and will eat half your repair budget if it is due.
Other engine issues (to google):
- Cam follower
- Cam chain stretch (block 92 or 93 in VCDS, can't remember)
- Coil packs
- Injectors
Other than that, it is really common stuff for any car. Clutch wear/bite, suspension knocks, brake discs, tyres, etc etc