Given that someone put a gash in it with a string trimmer, its likely stucco over rigid foam insulation panels.
If there's wire mesh in there as well, it's likely a traditional multi-coat stucco finish that can be repaired using stucco repair techniques.
If there's no wire mesh, you may have an EIFS wall (exterior insulation finishing system), which is kind of insulation and finish in one. This should be repaired using products and techniques specific to EIFS.
Answer from mac on Stack ExchangeVideos
Long story - got my BBQ to close to my townhouse and 2 panels of siding melted a little (yeah, I know bonehead move). It's about 2-3ft in length and I'll probably need to replace 2 panels. I've been looking online for a company that will sell 1-2 sheets, but everyone wants to sell me $500+ worth of it (which I don't need).
Any recommendations where to look? I live in MA (North of Boston) if that helps someone give me a recommendation.