Syntax

According to Wikipedia:

[A particular] meaning of the term syntax has been evolved in the field of computer science, especially in the subfield of programming languages, where the set of allowed reserved words and their parameters and the correct word order in the expression is called the syntax of language. This application of the word can apply to natural languages, as well, as through Latin's inflectional case endings.

In computer languages, syntax can be extremely rigid, as in the case of most assembler languages, or less rigid, as in languages that make use of "keyword" parameters that can be stated in any order. The syntax of expressions can be specified with parse trees. The analysis of programming language syntax usually entails the transformation of a linear sequence of tokens (a token is akin to an individual word or punctuation mark in a natural language) into a hierarchical syntax tree (abstract syntax trees are one convenient form of syntax tree).

Semantics

According to Wikipedia:

In the main, semantics (from the Greek and in greek letters "σημαντικός" or in latin letters semantikós, or "significant meaning," derived from sema, sign) is the study of meaning, in some sense of that term. It should not be confused with the general Semantics of Alfred Korzybski, a somewhat different discipline. Semantics is often opposed to syntax, in which case semantics pertains to what something means, while syntax pertains to the formal structure/patterns in which something is expressed (for example written or spoken).

Semantics is distinguished from ontology (study of existence) in being about the use of a word more than the nature of the entity referenced by the word. This is reflected in the argument, "That's only semantics," when someone tries to draw conclusions about what is true about the world based on what is true about a word.

Scalar

According to Wikipedia:

In mathematics, physics, and computing, a scalar is a quantity usually characterized by a single numeric value or not involving the concept of direction. The term is often used in contrast to entities that are "composites" of many values, like vector, matrix, tensor, sequence, etc.. The first recorded usage of the term was by W. R. Hamilton in 1846.
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In computing, a scalar is a variable or field that can hold only one value at a time; as opposed to composite variables like array, list, record, etc.. In some contexts, a scalar value may be understood to be numeric. A scalar data type is the type of a scalar variable. For example, char, int, float, and double are the most common scalar data types in the C programming language.