A pin Processor has metal pins on the bottom of it.
For an example let's use an Intel Pentium 4 processor, that fit in a Socket 478 processor socket.http://www.cpu-world.com/CPUs/Pentium_4/TYPE-Desktop%20Pentium%204%20Willamette.html
Viewing the link above, observe the green square under the grayish metallic looking square.
The green square is a circuit board.
(Width and length, about the length of your first digit on your thumb)
The grayish metallic square, is a metal shell cover over a Chipset.
Chip and Chipset are slang terms for I.C.
The Integrated Circuit here is the Processor.
The Processor is connected to the green circuit board. (PCB. Printed Circuit Board)
On the bottom of the green circuit board are contact pins. In this case 478 of them. (478 pins)http://www.cpu-world.com/CPUs/Pentium_4/Intel-Pentium%204%201.7%20GHz%20-%20RK80531PC029G0K%20%28BX80531NK170G%29.html
The tiny metal contact pins fit down into matching socket holes, in the processor socket.
A Socket 478 processor socket,http://en.wikipedia.org/wiki/Socket_478
(You can click on the photo to the upper right to enlarge it.
The next design to come out, has the Processor with contact pads, (Pinless), and the processor socket has the contact pins.
An LGA 775 processor socket,http://en.wikipedia.org/wiki/LGA_775
Example of a Pentium Dual Core's bottom side. (LGA 775 processor socket is used),http://www.cpu-world.com/CPUs/Pentium_Dual-Core/Intel-Pentium%20Dual-Core%20E2220%20HH80557PG0561M%20%28BX80557E2220%20-%20BXC80557E2220%29.html
There you have it.
A 'Pin' processor has metal contact pins on the bottom.
A 'Pinless' processor has metal contact pads.
For additional questions please post in a Comment.