Different terms in a contract (both express terms and implied terms) will clearly vary in their level of importance. Consequently the law seeks to classify terms according to their importance, with the implications of a breach for the innocent party varying according to the type of term breached.
For these purposes, there are three types of contractual term: conditions, warranties, and innominate terms.
Conditions
A term which is clearly an important one, in the sense that a breach of it would have very significant consequences for the innocent party, will usually be regarded by the courts as a condition. Where a condition is breached, the innocent party is entitled to regard the contract as repudiated, and so need not render any further performance, and can also sue for damages. In some cases, the parties themselves may have described particular terms as conditions in a written contract.
Warranties
Warranty usually describes a contractual term which can be broken without highly important consequences. If a warranty is breached the innocent party can sue for damages, but is not entitled to terminate the contract.
Innominate terms
These are also known as intermediate terms. They are terms which can be broken with either important or trivial consequences, depending on the nature of the breach. If the effects of the breach are serious, the term will act as a condition; if they are minor, it acts as a warranty.
One problem with innominate terms is their potential for uncertainty; until a breach has occurred, it may not be clear what kind of term is involved.