Ectenia is a special kind of prayer where one person says something and then everyone else responds in the same way. It's like a special song that people sing together, but instead of music, everyone says words.
The person who starts the ectenia, called the "chanter," says something like "Lord, have mercy." Then, everyone else responds by saying "Lord, have mercy" back to the chanter.
This pattern continues for many different things that the chanter may ask for help with, like "for the peace from above" or "for our enemies." Each time the chanter says something, everyone else responds in the same way.
The idea behind ectenia is that it helps everyone to focus and pray together as a group. It can be very powerful when done with a lot of people, especially during important religious ceremonies or events.
So, basically, ectenia is a special kind of prayer where a leader says something and everyone else responds in the same way. It helps people pray together and stay focused on what they want to ask for.