OP mostly likely means "weed" like "pest" or "annoyance", i.e. a category of undesirable plants that tend to appear unbidden along with desirable plants. The distinction isn't biological, it's just that when you create a space for growing then things that grow won't all be what you want.
(The term "weed" for marijuana is just a joke derived from that sense of the word.)
(The term "weed" for marijuana is just a joke derived from that sense of the word.)