Page 35 - Bob Holtzman "The Field Guide to Knots How to Identify.."

Elbow: Take a bight and twist it 360 degrees: the elbows are the two sections of

rope between the crossing turn at the top, and the working end and standing part
at the bottom.

Overhand and underhand: a crossing turn in which the working end is over
the standing part is known as “overhand,” as in the photo below. An
“underhand” crossing turn is the opposite, where the working end is under the
standing part, as in the photo above. The crossing turn may be above or below
the run of the rope. If you turn an overhand crossing turn over, it becomes
underhand.

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