* BC (Before Christ): This is used for years before the birth of Jesus Christ. For example, 100 BC means 100 years before the birth of Jesus Christ.
* AD (Anno Domini): This is used for years after the birth of Jesus Christ. For example, 2023 AD means 2023 years after the birth of Jesus Christ.
* CE (Common Era): This is a secular alternative to AD and is used to avoid religious connotations. It is equivalent to AD. For example, 2023 CE means 2023 years after the birth of Jesus Christ.
* BCE (Before the Common Era): This is a secular alternative to BC and is used to avoid religious connotations. It is equivalent to BC. For example, 100 BCE means 100 years before the birth of Jesus Christ.