Which music notation indicates holding a note slightly louder playing a note slightly louder or holding a note for its original length?

Especially in the days before audio recording and playback, music was often written out as a means of preserving and communicating it. To do this, a system of notation was developed that gives musicians the information they need to play music as the composer intended it.

(Hope it helps :) )

Tenuto

Explanation:

The tenuto, is a duration direction used in the musical notation. It means to "hold" or sustain a note for its full length. At the end of the far right, a line over or above the body of a single line note means it is to be played tenuto or held to its full value. A single dot above or below the body of a note means its staccato, or short and separate.