IsA (Function)
From Legacy Roblox Wiki
IsA is useful for figuring out if an object is a specific type of object. For example, if you do Part:IsA("Part") it will return "true".
Example
This can be used to find a part in a list of objects.
children = script.Parent:GetChildren() for i=1, #children do if children[i]:IsA("Part") then print(children[i].Name .. " is a Part object.") end end