Jenny
It's the letter "Eth" in Old English.
Ð (capital letter); ð (small letter)
It has a 'th' sound - often like the 'th' in the word - the; but occasionally it has the softer 'th' sound as in the word - thing.
HERE
This is the other 'th' sound - called "Thorn":
Þ (capital letter); þ (small letter)
-------------------------------------------------------------------------
You can access these letters and many others using a tool program on your computer:
Just click on these steps in this order.
Start --- All Programs --- Accessories --- System Tools --- Character Map
Or, you can do this:
Alt key+0240 = ð