They are called an audience or attendees.
an audience
A group of people listening to a lecture is commonly referred to as an audience.
audiance
A group of people gathered to hear or see an event or performance is typically referred to as an audience. This term is commonly used in settings such as theaters, concert halls, or lecture halls where individuals come together to watch or listen to a specific presentation.
It is a "collective Noun"
A Flock
people gathered at this place because this is the place that you can read lots of books and you can get knowledge by reading books on the library.
The word form for lecture is a noun. It refers to a formal talk given to a group of people, typically in a university or educational setting. The word "lecture" can also be used as a verb, meaning to give a formal talk or presentation to an audience.
A stab in the light.
When you are 18 or older, you start to become a mature adult and start to take care of yourself normally.
congregation
A crowd.