Historically the terms have been fairly interchangeable, however modern historians in an effort to save immense confusion amongst themselves have opted to generally accept the lance to be specifically a long spear on horseback intended for melee rather than throwing
Lance
A spear is a type of lance.
The Spear of Destiny (Holy Lance, Lance of Longinus, Spear of Longinus) have name for lance that pierced the side of Jesus when he hung on the cross.
A lance in the original sense is a light throwing spear.
My thesaurus lists stick or stab. The noun "lance" is related to spear.
Spear is a synonym for lance. It begins with the letter S.
'Spear'.
spear
lance
lance
She had a long lance or spear.
Lance.