I'm not actually sure if we are supposed to talk religion or politics on this site, but if you look at the Bible as a historical reference...
The word itself is not in the Bible.
The phrase " sensual pleasure" however, is...but it doesn't say anything about pleasing oneself...it says: " You have lived in luxury upon the earth and have gone in for sensual pleasure."
I have talked to people of many faiths, and they all have their own theories on this category.
Some assume that Priests may not masturbate...but their faith only says that it's better to be either celibate OR to marry. Celibate means to not have sexual intercourse with a woman/man...it doesn't mean not to masturbate.
The Jehovah's Witnesses believe that masturbation is a sin...that you should save any and all sexual practices for marriage. They believe that if you masturbate then you won't submit to your spouse.
Some religions don't or won't tell you much either way.
So...I guess it really depends on which religion you talk to.
I have searched, and this is what I found:
"Marriage should be honored by all, and the marriage bed kept pure, for God will judge the adulterer and the sexually immoral" (Hebrews 13:4, NIV).
"Marriage is honorable in all, and the bed undefiled: but whoremongers and adulterers God will judge" (Hebrews 13:4, KJV).
Same verse, but from different Bibles.
Now you must decide for yourself how to interpret these.
There are many sites dedicated to Bible interpretations...try searching them for your answer.
Um, I don't think you're supposed to in the Bible cause that's what your husband is for. You're just supposed to have sex with your husband in the Bible. It doesn't give specifics but I don't think it was a done thing- to masturbate.
My Bible says that anything you can "wash" your hands after is fine.