I've seen these all used somewhat interchangeably. What's the difference?
I've seen many
\start..stop blocks referred sometimes referred to as environment. For example the verbatim environment for
\start...stoptyping block. Some are even ambiguously named like
\start...startsectionblockenvironment. Then there's the big picture. Is
\start...stoptext an environment or a block? Excursions says this in section 40.5, Floating Blocks:
A block in CONTEXT is a text element, for example a table or a figure that you can process in a special way. You have already seen the use of
\placetable. These are both examples of floating blocks.
Where does that leave regular paragraphs? From the wiki I get the sense that colloquially blocks imply 'more' vmode whereas environments can be either vmode or hmode. So
\start..stoptextbackground is an environment rather than a block because it can be used inline?
What do you call a clump of text that forms a semantic element, a higher-level view than characters, glue and boxes? On a tangent I came across TeX 'groups' and, knowing nothing of them, decided perhaps they could be related to this question.