What is the difference between an ordinary 2-form and just a 2-form in general? Cant seem to find the definition for ordinary 2-form anywhere.
Thanks in advance!
Edit: If it helps, it was used in the following context: 'Since U(1) is abelian, for any U(1) line bundle L over M, ad(L) is the trivial bundle $M \times i \mathbb{R}$. So the curvature f of a connection d' is an ordinary 2-form.'
Generally a connection and its curvature are Lie algebra valued differential forms, a particular case of vector valued differential forms,see e.g. https://en.wikipedia.org/wiki/Vector-valued_differential_form . For the Lie group $U(1)$ the Lie algebra is isomorphic to the real numbers so you get what they call an ordinary (real valued) differential form.