This is probably a silly question, but I cannot find the answer anywhere. What do these symbols mean?

 

I also wish to know.

 

the symbols you have numbered as 2 and 3 are numbered 1 and 2 in picture above. They represent a contact which is 'shorted' to another contact, UNTIL the plug is inserted in the jack. When this occurs the symbol with the 'v' shape is pushed away from the other contact and is no longer electrically connected with it. It is then in contact with the plug that has been inserted.

As for the one you have labeled number 1, it is not a symbol I am familiar with but from its looks, I would guess it to be the 'plug' that one places in the jack(socket).

 

Just to rephrase and embellish what Kermit2 said, it's a coaxial DC power jack. Pin 1 is the center post. Pin 2 is the switched contact that usually comes from the batteries in portable devices. Pin 3 is the barrel connection that supplies the circuit needing power (from the switched contact when no plug is inserted or from the external power supply when the plug is inserted.

Here's a catalog datasheet: http://www.mouser.com/catalog/specsheets/KC-301286.pdf.

The Wikipedia article is surprisingly long and detailed: http://en.wikipedia.org/wiki/Coaxial_power_connector.