A weed is a plant considered undesirable in a particular situation, “a plant in the wrong place”. Examples commonly are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns, and parks.
Taxonomically, the term “weed” has no botanical significance, because a plant that is a weed in one context is not a weed when growing in a situation where it is in fact wanted, and where one species of plant is a valuable crop plant, another species in the same genus might be a serious weed, such as a wild bramble growing among cultivated loganberries.
Many plants that people widely regard as weeds also are intentionally grown in gardens and other cultivated settings, in which case they are sometimes called beneficial weeds.
The term weed also is applied to any plant that grows or reproduces aggressively or is invasive outside its native habitat (source)
Can guinea pigs eat garden weeds?
It really depends on what they weed is. Rule of thumb is that if you are in doubt don’t feed it to them as there are so many to name. Avoid anything you know is poisonous such ivy.
For more foods that guinea pigs can and can’t eat, check out our guinea pig food list