This is mostly for the sake of blade ward, and other effects, that state:
You have resistance against bludgeoning, piercing, and slashing damage dealt by weapons.
However, traps may include things like arrows, spears, maces, flails, and other such things. Does the fact that they are made into traps mean that blade ward is only effective when a person is wielding the weapon?
Are things that could be weapons, but are normally not, considered in the same way (like stones)?
Or is the answer specific to each trap, like if blade ward can work against a flail trap, but can't work against fall damage (which both do non-magical bludgeoning damage)?
Best Answer
The quote you give for the effect of blade ward lacks the most important word in answering this question:
"Weapon attacks" is a well defined phrase in D&D 5e, and refers to all things which are attacks and not spells, approximately. The important thing here is that some thing cannot be a weapon attack if it is not an attack; "weapon attack" is a special type of "attack".
Whether or not a trap makes an attack is covered by a previous question. Short version: if it makes an attack roll, then it's an attack. If the description states that it is an attack, using the exact word "attack", then it's an attack.
As mentioned earlier, some spells also require attacks, and those are "spell attacks". Other attacks are "weapon attacks". I haven't found a perfect explanation for how to distinguish 100% of the time, but I would say that if a spell calls for an attack roll, or an ability uses the exact phrase "spell attack", then it's a spell attack. Note that attacks with magic weapons are still weapon attacks even if they deal magical damage.
If a trap meets both requirements, i.e. it is an attack and it is not a spell attack, then blade ward would provide resistance against its bludgeoning, piercing, and slashing damage.
For example, here is the first trap I could find on dndbeyond, the Hunting Trap:
The Hunting Trap requires a saving throw in order to avoid the effect. It does not make an attack roll, so it is not an attack and blade ward will not grant resistance against its damage.