This property determines an object to be ignored by the mouse when calculating Mouse/Hit and Mouse/Target. The descendants of the object are also ignored, so it is possible to ignore multiple objects so long as they are a descendant of the object to which this property is set. This property is useful when filtering models containing special effects or decorations that should not affect Mouse/Hit or Mouse/Target.

This property can be set to any Instance or nil, for example:

local Players = game:GetService("Players")
local player = Players.LocalPlayer 
local mouse = player:GetMouse()
mouse.TargetFilter = workspace.Model
 
-- Now, when the player hovers the cursor over the model, mouse.Target will be some object
-- behind workspace.Model, if there is one.

This property is essentially a single-object blacklist for mouse raycasting. For more in-depth control on raycasting, see the following functions of Workspace: Workspace/FindPartOnRay|FindPartOnRay, Workspace/FindPartOnRayWithWhitelist|FindPartOnRayWithWhitelist and Workspace/FindPartOnRayWithIgnoreList|FindPartOnRayWithIgnoreList.

The Player/Character|Character of the Players/LocalPlayer is ignored by the mouse automatically.