What is perjury and how to spell it?

I've become too accustomed to having my spell check catch my typos and memory lapses (don't have it for FB on my old computer). Today I couldn't remember how to spell PERJURY. I tried purgery, and purjery--and even my spell check which underlined it couldn't figure out what I wanted to say. Nothing looked right. But I knew what it was--the offense of willfully telling an untruth in a court after having taken an oath or affirmation. It's a bit more expansive in the U.S. Code than the dictionary.

Whoever—

(1) having taken an oath before a competent tribunal, officer, or person, in any case in which a law of the United States authorizes an oath to be administered, that he will testify, declare, depose, or certify truly, or that any written testimony, declaration, deposition, or certificate by him subscribed, is true, willfully and contrary to such oath states or subscribes any material matter which he does not believe to be true; or

(2) in any declaration, certificate, verification, or statement under penalty of perjury as permitted under section 1746 of title 28, United States Code, willfully subscribes as true any material matter which he does not believe to be true; is guilty of perjury and shall, except as otherwise expressly provided by law, be fined under this title or imprisoned not more than five years, or both. This section is applicable whether the statement or subscription is made within or without the United States.

So, is it perjury if the person is incapable of telling the truth, as Mrs. Clinton appears to be? Is it perjury if her chief of staff hid 650,000 emails on her husband's laptop when Mrs. Clinton said under oath she only deleted 33,000? She believes her lies to be true.