What is a dative covalent bond?

A dative covalent bond, or coordinate bond, is a bond where there is 1 pair of shared electrons between two atoms. The difference relative to a covalent bond is that in a dative covalent bond these electrons both come from one atom.
An example of this is the ammonium ion, NH4+. One of the single bonds between the nitrogen and hydrogen will be a dative covalent bond.
Dative covalent bonds have the exact same orbital shapes and repulsion as normal covalent bonds. Ammonium, like methane, would therefore have a tetrahedral shape with bond angles of ~109.5°.
Dative covalent bonds are represented on drawings as an arrow, with it pointing towards the atom/ion that isn't donating any electrons to the dative covalent bond.