People sometimes give me phone number like (XXX) XXX XXXX ext. XXX. I was wondering what does this 'ext. XXX' mean?

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    extension, a line within the phone system at that number. – user3169 Feb 11 '16 at 18:44
  • Do I dial all the numbers at the same time? – Lii Feb 11 '16 at 18:45
  • You only dial the (XXX) XXX XXXX number. After the call is answered you would say or enter the extension number. – user3169 Feb 11 '16 at 18:49
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    This should be looked up in a dictionary. ext or ext for example. – user3169 Feb 11 '16 at 18:53
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    @user3169 - Given the context, and the five available options, it's not inconceivable that the "ext." would stand for "extra" (as in, "extra digits"). I'm just trying to look at this like a learner might. Moreover, looking up extension in this same dictionary, it says, "an extra telephone connected to the same line as the main telephone." I'm not sure that that would provide a crystal-clear answer, and I don't think ELL is a bad place to ask for clarification. – J.R. Feb 12 '16 at 0:34

ext. is short for extension which is an internal number used within a PBX systems.
It is usually an additional short number and may or may not be related to the originally dialled number.

The extension number is usually requested and dialled once the caller is inside the local PBX system.

Users within the PBX can call each other by using only the extension number.

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