A 
tail is the decorative stroke on the letter 
Q. It can also be found on the capital letters
 R and 
K that have a decorative stroke. On the letters 
g,
 j, 
p, 
q, and
 y the descender is also called a tail.
Fonts used - Monotype Corsiva (for the words), Perpetua Titling (to create the mice with the letters Q, O, and V).
And if you're still confused about tails:
images © Kelci Stephenson 2011