Many different types of trusts exist. Some are business related, and some are personal trusts.
One focus of this website is the subject of personal trusts. Business trusts, which may be used to organize mutual funds for example, is not is not subject today.
A 'Trust' is a relationship
A trust describes a legal relationship between a trustee and one or more beneficiaries. some people think that it is a legal entity - like a corporation or a partnership.
Instead, legal scholarship tells us it is a relationship and not an entity.
The trustee owes a duty to the beneficiary to follow the terms of the trust. (The written trust document is usually the controlling terms - although an oral trust can also be valid.)
Types of trusts
Trusts contains many terms. It is likely that a good trust will be many pages long, likely over 20 pages.
One of those terms will be to state if the trust may be changed or not. The words used are revocable or irrevocable.
But remember that within these two categories, many variations exist. These varying terms, beyond the revocable vs. irrevocable single term, that determines the heart of the matter.