The fourth is what restrictions. Term is fairly self evident. What is covered is more detailed. Often mechanical components such as tape heads are covered by different terms, such as shorter terms on labor and longer terms on parts. Likewise, speaker warranties vary widely, from unconditional with no term limit to a basic 30 days parts and labor.
Some warranties come from the manufacturer.
Others come from the dealer. Still other warranty support is available with certain premium charge cards. A common restriction on some warranties is that the equipment is not covered unless it is sold by an authorized dealer. A few dealers have lied about being authorized dealers. Equipment sold by an unauthorized dealer is almost always sold completely legally.