What exactly means Concurrency in Apache Bench?

Question

I use Apache Bench for test some applications performance. I try to send 10 requests with concurrency = 3. I understand that concurrency 3 means that Apache Bench opens 3 TCP connections with my application. For example:

I suppose that I have 3 TCP connections with 3 requests [1,2,3]. Apache Bench first sends request 1. So my new requests will be [4,2,3].

Next Step:

1. Will Apache Bench wait until get a response from request 1 and after send request 2?
   I mean that the flow of requests will be: 1 ->response1->2->response2 ...... ?

OR

2. Will Apache Bench send request 2 without wait the response of 1?
   I mean that the flow of requests will be: 1-> 2 -> response for request 1 -> 3 ....

What really applies?