From MTG Salvation Wiki
"Mana screw" is a term that refers to the condition of not having enough
mana (or not having the right color of mana) to play the spells in your hand. Mana screw can be the result of several factors: poor luck; an opponent playing a strategy to reduce your mana (such as
land destruction and other forms of mana denial); or poor judgement, not having enough mana sources in your deck.