Beyond the clarity grading terms, other considerations include the type, size and location of an inclusion.  Inclusions near or on the surface may weaken the diamond structurally.  Depending on where the inclusion occurs in the cut diamond and how it is to be used, it may be possible to hide the inclusion behind the setting.
I didn't know that did you?  I think most of us have heard of flaws, not inclusions.

Laser "drilling" involves using a laser to burn a hole to a colored inclusion, followed by acid washing to remove the coloring agent.  The clarity grade is the grade after the treatment.  The treatment is considered permanent and both GIA and AGS will issue grades for laser drilled diamonds.  Reputable vendors should disclose that laser drilling has been used.

Clarity can also be "enhanced" by filling the fracture much like a care windshield crack can be treated.  Such diamonds are sometimes called "fracture filled diamonds". These are less expensive.
Reputable vendors must disclose this filling and reputable filling companies use filling agents which show a flash of color, commonly orange or pink, when viewed closely.  Fracture filled diamonds are not graded, because the filling isn't as permanent as diamond.  Reputable companies often provide for repeat treatments if heat causes damage to the filling.  The heat required to cause damage is that of a blowtorch used to work on settings, and is essential to inform anyone working on a setting if the diamond is fracture-filled, so they can apply cooling agents to the diamond and use greater care when working on it.