What is the meaning of the half blood prince?

I just saw Harry Potter and the Half-Blood Prince. I do not understand. Why was it so important that half blood prince was Snape?

If you have not read the books, I can see why you ask this question. "So Snape is the half blood prince, big deal. "It's a big problem because in the book, Harry looks into the memories of growing and discovers that Lord Voldemort is actually a half-blood. Throughout the book, they assume that the half blood prince is Lord Voldemort and Harry uses his book. So when Snape shows he is the half blood prince is a major shock.

‘Harry Potter and the Half-Blood Prince’ Trailer 4 HD

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE SECRETS REVEAL $9.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE HARRY SPELL $5.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE DUMBLEDORE $5.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE ASK TOO MUCH $9.95

Harry Potter & The Half Blood Prince BLK T-SHIRT M NWT! $4.99

Harry Potter & The Half Blood Prince BLK T-SHIRT L NWT! $4.99

Harry Potter & The Half Blood Prince BLK T-SHIRT XL NWT $4.99

Harry Potter & The Half Blood Prince 2XL T-SHIRT 2X NWT $4.99

Harry Potter & The Half Blood Prince SKINNY T-SHIRT L $4.99

HARRY POTTER LOCKET FROM THE CAVE HALF BLOOD PRINCE NEW $59.95

1st PRINT HALF-BLOOD PRINCE HARDCOVER $4.99

1st PRINT HALF-BLOOD PRINCE HARDCOVER $1.99

Harry Potter Half Blood Prince Cards $0.99

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE TRIO CAST $6.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE REFLECTION $6.95

HARRY POTTER LOCKET FROM THE CAVE HALF BLOOD PRINCE NEW $59.95

HARRY POTTER THE HALF BLOOD PRINCE HORCRUX RING NEW @@@ $59.95

Harry Potter Necklace-Half-Blood Prince release 2009!! $11.00

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE DUMBLEDORE $9.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE UNDERGROUND $9.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE HERMIONE STAIRS $9.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE HARRY ON GUARD $5.95

Harry Potter Half-Blood Prince ORIG THAI poster &BONUS $9.77

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE MOVIE 4 CAST $6.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE HERMIONE STAIRS $6.95

Harry Potter and the Helf-Blood Prince Keepsake Box $15.99

Harry Potter and the Helf-Blood Prince Keepsake Box $15.99

Harry Potter and the Half-blood Prince by J. K. Rowl... $19.99

Harry Potter Half Blood Prince Promon Pack Sam's Club $2.22

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE UNDERGROUND $6.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE MOVIE 4 CAST $6.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE HERMIONE STAIRS $6.95

HARRY POTTER & THE HALF-BLOOD PRINCE - 1st Ed - H/B $7.70

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE DARK ARTS SPELL $6.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE CAST COLLAGE $5.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE WAND ADVANCE $9.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE SEVERUS SNAPE $9.95

NEW Harry Potter and the Half-Blood Prince (S1) Mini $29.95

NEW Harry Potter and the Half-Blood Prince™ (S5) $29.95

NEW Harry Potter and the Half-Blood Prince™ (S3) Trio $99.95

NEW Harry Potter and the Half-Blood Prince™ (S1) Double $62.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE TRIO CAST $6.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE REFLECTION $6.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE DUMBLEDORE $9.95

H.POTTER AND THE HALF BLOOD PRINCE 3-D POSTER 11X17 $8.50

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE MOVIE 4 CAST $6.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE HERMIONE STAIRS $6.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE SECRETS REVEAL $9.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE HARRY SPELL $5.95

HARRY POTTER POSTER ~ HALF-BLOOD PRINCE DUMBLEDORE $5.95