Use of [H] to denote a reducing agent

In the reduction of an aldehyde (e.g. ethanal) to a primary alcohol, a reducing agent is needed:
$$\ce{CH3CHO + 2[H] -> CH3CH2OH}$$
My book states that one hydrogen (the $\ce{H-}$ ion) is from the reducing agent, and the other hydrogen (the $\ce{H+}$ ion) is from the solvent.


However, elsewhere it more generally notes that "$\ce{[H]}$ denotes a hydrogen from a reducing agent".


Does the $\ce{[H]}$ notation refer only to hydrogen atoms from the reducing agent, or, as this example implies, can it also refer to hydrogen atoms from other sources (such as the solvent)?


