Empress
Empress Consort, Queen
noun
The kanji and the word are exactly the same, so this means empress.
后 specifically refers to the wife of a male ruler, rather than the sort of empress who might rule a country herself. In ancient Japan, it referred to the emperor's highest-ranking wife — the empress consort — but you'll also see it used in non-Japanese contexts to refer to a king's queen.
Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word:
To become the empress, you need to kiss a king (きさき). Well, technically you need to kiss an emperor, but you can start by kissing a king and then work your way up.
お后様がりんごを落として潰してしまったんです。
Her Majesty dropped the apple and squashed it.
后は静かに玉座の横に座っていた。
The empress consort sat quietly beside the throne.
その国の后は民に深くしたわれていた。
That kingdom's queen was deeply loved by the people.
后の姿が見えると、侍たちは一斉に頭を下げた。
When the empress consort appeared, all the samurai bowed all at once.