Answer:
Two covalent bonds between adjacent atoms in a molecule
Step-by-step explanation:
A covalent bond is a pair of electrons shared between adjacent atoms, so a double (covalent) bond is two pairs of electrons shared between adjacent atoms.
We usually represent a covalent bond by a line, so a double bond is two lines between adjacent atoms, as in H₂C=CH₂.
Two separate single bonds are NOT a double bond.