A foreign object in first aid terms, relates to an object of any size that enters the body through many of its orifices, or penetrates the skin and is embedded.
You have to make a decision on whether you can remove it without having to seek medical help.
If a common embedded object such as a splinter is partly exposed, then it is acceptable to remove it with tweezers.
First aid tweezers generally come in a sterile package. Washing grit away, under running water, can also be a useful treatment. If this won’t remove the object, then the wound should be dressed with a sterile dressing, without putting direct pressure on the object, and then to seek medical attention.
However, for other objects such as glass or a fishing hook, they must be left in place and you should not attempt to remove it. Dress the wound appropriately and seek medical advice.