FYI: Gravel and pebbles describe the same type of stone, naturally rounded by erosive processes whereas the correct term for sharp edges (artificially broken) material is “crushed stone”. Nevertheless "gravel’ is the common term used for all kinds of small stones of a size roughly in between 2 - 80 mm and any road or track with a surface of such stone, may it be rounded or sharp edged, compacted or loose is called a “gravel road” in common english. For more details have a look here.
A sample pic for pebbles:
A sample pic for gravel:
Any difference?
And here is a pic of a nicely compacted road:
which is called “gravel road” nevertheless.
And another pic of a road with loose gravel surface (as seen above)