If you're looking for a single source you can go to for a definitive understanding of the Enneagram then you'll likely be disappointed or misled.
Although there is consensus agreement on many things about the Enneagram types and related concepts, the more you dig the more you'll find subtle and even not so subtle differences as well.
While people who write about, teach, or provide consulting using the Enneagram may see themselves as experts or authorities on the subject, they're really only experts or authorities on their interpretation of the Enneagram.
Each author of the Enneagram types has their own interpretation. If they didn't then there would be little point in writing another book about the types.
There is both common overlap and differences between these interpretations. Differences may have to do with how the types are described or the concepts used.
Training and certification is offered by a number of different sources. This often includes teacher training and Enneagram coaching certification. Students of each school will tend to propagate that school's teaching through their own teaching, coaching, and other offerings.
So although you may see a similar take on the Enneagram types on multiple websites, often it's just the same take from the same source school by a different student. It doesn't mean it's authoritative. It just means that school has been successful at finding and training students.
The names given to the types can be indicative of which interpretation is being used or has had an influence on what you're reading. In an attempt to distinguish themselves from one another, different schools tend to use different names. The names of the older and more successful schools are the ones you'll see most often.
To avoid any bias or confusion it's best to simply use the type numbers instead of any names. The names only describe one aspect of a type and that in itself might be misleading. Also, if you use a name then people who only use the numbers or aren't familiar with that name likely won't know what type you're talking about.
In addition to the basic type, variations of type are often used. Type variations are additional influences on type that create differences between people of the same type. Common concepts used to describe these variations are wings, instincts, subtypes, and centers.
Not all variations are emphasized by all teachers and schools. Some variations are widely accepted while others aren't. Not all people interpret or describe these variations in the same way.
Related Article: The Enneagram describes 9 basic personality types. Is 9 enough?
One reason you may get different results on different tests is that each test uses it's own interpretation of the types. Even when the interpretations are similar there can be different emphasis on which characteristics are most important for a given type.
For this reason it's a good idea to use the type descriptions specifically associated with a test when exploring your test results. If you don't know the specific interpretation being used then try to use the type descriptions from the website where you took the test.
Sometimes you may see something about an "official" test. It's important to know there really is no "official" Enneagram test. It's official only in the sense that it correlates to a particular interpretation of the types.
When someone has originated or trademarked a particular approach to the Enneagram types then "official" might mean that the test has been created by the originator of that idea or owner of the trademark.
People sometimes describe themselves as Enneagram experts. What they may be expert in is their particular interpretation of the Enneagram types.
"Expert" doesn't guarantee that their opinion will be more accurate than someone else's. It may just be different.