Can a server be the one contacting the client without the client making a request first?

It seems for the TCP/IP protocol, the client need to be the one sending a request to a server for the server to send a response.

1) I wonder if let's say the server knew every client IP addresses. Would it be possible for the server to send data/response/content to clients without clients making any request to that server first?

2) In other words, what make the client different from a server. Why server can receive any requests from any client but client cannot receive any requests from any servers ?

3) And when a client do send a request to a server. Does this request is unique? For example, if the client send a request to a server, can the server send thousands of response instead of just one?

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For you expert in networking, it's probably all dumb questions but i'm so curious about it.