Hardness
Graphite pencils are graded for the hardness (H) or blackness (B) of the graphite. The harder the pencil (rated H to 9H) the lighter the marks on the page.
The softer the pencil the more dark or black the marks (B to 9B) will be.
HB is the "middle" pencil if you like, and the one we all used at school for writing and drawing.
Here is a graphite drawing made with a few of those pencils.
