Answer:
side-by-side, or lateral orbital overlap with the electron density concentrated on opposite sides of the internuclear axis.
Explanation:
Pi bond is a type of covalent bond in which the internuclear axis has regions of orbital overlap below and above it i.e on opposite sides. As a result of the orbital overlap, a node is created along the internuclear axis.
This ultimately implies that, a pi bond is formed due to the lateral (side-by-side) overlap of the unhybridized P-orbital comprising of at least a node along the internuclear axis.
Hence, a pi bond involves side-by-side, or lateral orbital overlap with the electron density concentrated on opposite sides of the internuclear axis.
Additionally, a node is typically formed where an electron cannot be found.
