“Plants (not necessarily alien) that grow in sites where they are not wanted and which usually have detectable economic or environmental effects (synonyms: plant pests, harmful species; problem plants). ‘Environmental weeds’ are alien plant taxa that invade natural vegetation, usually adversely affecting native biodiversity and /or ecosystem functioning.” (Richardson et al., 2000, p. 98)
“A plant that is a pest in a particular circumstance.” (IPBES)
Source/reference: Richardson et al., (2000, p 98). https://www.ipbes.net/glossary-tag/pest