Jacob's thigh was disabled by the Angel, to show the patriarch that his prevalence was through his faith and prayer, not through force, Genesis 32:25-31. Smiting the thigh was a gesture of self-condemnation and grief, Jeremiah 31:19 Ezekiel 21:12.
In general, a datum is a base elevation used as a reference from which to reckon heights or depths. A tidal datum is a standard elevation defined by a certain phase of the tide.
Quick Answer. A datum line is a point of reference or standard for comparison. The term is primarily used in reference to surveying and engineering, where it is used in the measurement of depths and heights. Continue Reading.