I spend a lot of time writing technical documents which need to be clear, consistent and unambiguous. These are a few terms that are often used inconsistently. The world would be a better place if we all used them properly... or at least our documents will look more consistent if we did.
The term "Web" should be capitalised when it refers to the World Wide Web. This is endorsed by Tim Berners-Lee. He is the person who invented the Web, so he ought to know.
The term "email" should be written without a hyphen. I used to always write it with a hyphen. But since Donald Knuth says drop the hyphen, then the hyphen is dropped! Who is Donald Knuth you ask? Knuth is my homeboy.
When describing PKI, "certificates" contain a public key and other information, which is all signed by a certificate authority (unless it is self-signed). Usually, certificates are in X.509v3 format. Many documents and software incorrectly refer to the private key and/or public key as certificates, and that just makes PKI even more confusing since the user needs to treat these things differently. Identity distinct items using distinct terms: certificate, public key, and private key. Never use one term to mean something else.
In computer security, digital signatures are verified and certificates are validated. Sometimes the terms are interchanged, but it is important to use them consistenly to prevent confusion. The correct terms are defined in the IETF RFC 2828 Internet Security Glossary. Always verify signatures and validate certificates.
When referring to XML documents, it is valid if it is well formed and conforms to a DTD. An XML document is called schema valid when it is well formed and conforms to an XML Schema (which some people call an XSD). The term valid (by itself) always refer to DTD validation and never to XML Schema validation.