A
linguistic concept.
Syntax is the way how words are combined to phrases or sentences. Syntax is commonly defined as a set of rules, which, if followed, are capable to produce all possible sentences (or programms if you consider computer languages as well) of a specific language correctly.
There are
psychologists that assume that there has to be a
syntax in our brains to understand language at all.
One (possible) rule of
the english language: "In declarative sentences the word order is subject,
predicate, object", e.g. Tom (subject) is sitting (predicate)
on the chair (object).