a flat slab of stone or wood: a writing tablet, or a board or plank
At its core this word names a flat, smooth slab. Whether the slab is stone or wood, and whether it is meant to be written on or built into something, depends on the setting.
Its most famous use by far is the writing tablet. When God gave the Ten Commandments at Sinai, he wrote them on two slabs of stone, and the Hebrew word for those slabs is this one. From there the word stretches to any flat surface meant to carry a written message, including the prophet's tablet on which a vision is recorded so it can be read at a glance, and the figurative tablet of the heart, where loyalty or sin is described as written deep inside a person.
The same word also names a plain flat board or plank used in building: the boards of the bronze altar, the panels set into the stands that held the temple basins, a cedar board fixed against a wall, and the deck planks of a ship. These uses share the literal picture of a flat slab even though nothing is written on them, which is why one Hebrew word covers both the stone tablets of the law and the timber of a ship's deck.