A centuria was a group of people in ancient Rome, kinda like a team or a group of friends. The group would usually have about 100 people, which is where the name "centuria" comes from (because "cent" means "100").
Centurias were really important in Roman society because they were used for military purposes. Each centuria would have a leader called a centurion who was really strong and smart. These centurions would lead their centuria into battles and make sure everyone knew what to do.
The Romans thought it was really important to have strong and organized groups like the centurias because it made it easier to win battles and protect their city. It also helped them work together to achieve their goals, kinda like when you and your friends work together to build a really cool fort or win a game.
So, in summary, a centuria was like a team of 100 people in ancient Rome that had a leader called a centurion. They were important for the Roman military and helped them work together to achieve their goals.