Yes – it’s a weird one. If you are asking about ‘bags of mulch’ or ‘wheelbarrows of mulch’ aka biodegradable mulch … it can mean any mix of these:
*DIY compost that hasn’t completely decomposed
… that kinda thing!
Sometimes people are referring to non-biodegradable mulch (although I wouldnt call it ‘mulch’ as they have quite a different purpose)
*crushed egg shell
ummm (abi) … interesting one. Im sure that thhere are people who would argue both sides. Me personally – i mulch:
1) when im prepping an area (or resting it)
2) around my big shrubs in the summer to help them retain moisture