A strait is a narrow strip of sea between two pieces of land. The Strait of Hormuz is beside a country called Iran. Big ships carry oil through it.
Last week we asked: would more ships get through, or fewer? The answer is fewer. A company that tracks oil said about two thirds as much oil got through this week as usual.
It linked this to more military action by Iran nearby. UK officials said ships have been attacked there. When less oil gets out, oil costs more. This week one barrel cost about $108.