# M branes/D branes are solitons?

I'm really confused.

In M theory/String theory, the fundamental objects are M/D branes. However, branes by defintion are just solitons. Solitons are just waves that maintain there shape.

So if a brane is a soliton wave, then what is it a wave of? Would it be the excitation of a field?

But a D-brane is not defined as a solitonic object at all, it's defined by the Dirichlet conditions for some open strings. That it corresponds, under some dualities (most straightforwardly reduction of M-theory to type IIa string theory), to such solitonic objects as the M2- and the M5-branes is a highly non-trivial insight. Most D-branes also actually correspond to solitonic solutions of the low-energy 10d SUGRA associated to the respective string theories in which they occur. Also, not all the solutions D-branes correspond to are M-branes, for instance, the M-theory dual of a $D_6$-brane is a Kaluza-Klein monopole/Taub-NUT space. Whether we want to call the Taub-NUT solution a "soliton" I'll leave to the reader to decide.