[Definition] The head collar is very similar to a halter on a horse. The theory it is that if you have control of the head, you have control of the body. The head collar generally consists of two loops, one behind the ears and the other over the nose. This tool makes it more difficult for the dog to pull on its leash. This is a management tool only, it does not train the dog not to pull. [Tool] 
Head collar
T r a i n i n g c o l l a r
P r o n g c o l l a r o r p i n c h c o l l a r
R a d i o - c o n t r o l l e d c o l l a r s
M a r t i n g a l e c o l l a r
H e a d c o l l a r
N o - p u l l h a r n e s s
D o g b i t e t u g