What does “Nine Pieces of Eight” mean?

Can anyone explain to me what the phrase "Nine Pieces of Eight" means? I understand that it took 9 pirate lords to bind Calypso, and the movie also shows the 9 pieces. However, what is this statement? What does it mean? Why is this important?

• Do you know what a "piece of 8" is? en.wikipedia.org/wiki/Spanish_dollar – Catija May 5 '16 at 17:34
• Yeah. What she said. You can have any number of pieces of eight. Even eleventy-one! You can also have 9 inches of one or six degrees of 2. It's just math. – Meat Trademark May 5 '16 at 18:39
• @MeatTrademark Catija is a she? – Vishwa Jan 22 '18 at 12:38
• @Vishwa, well, in the public-facing profile she created with the full expectation that people would look at it, she indicates both how to pronounce her name and what her preferred pronoun preference is. – James McLeod Oct 22 '18 at 9:51
• @vishwa then maybe you should be too lazy to question someone’s use of female pronouns too? :-) – James McLeod Oct 22 '18 at 10:20

It’s a Spanish silver coin worth 8 Spanish reales. So the 9 pirates would break the coin (worth 8) into 9 pieces. One piece of the coin for each of the 9 pirates. So basically 9 pieces of a coin worth 8 of it’s face value.

In the movie, the crew/swabbies were confused because it wasn’t a coin, instead it was items or junk. It is explained when they collect the pieces, the plan was to use 9 pieces of 8 (silver coin), but when the Brethren court met they were, well, broke! So they improvised;

“Nine pieces of whatever we happen to have in our pockets at the time!”