juxtaposition

In mathematics, juxtaposition of symbols is placing them sequentially without an interrupting operator, space, or other symbol.

For example, the juxtaposition of $a$ with $b$ would be written $ab$.

In a numeral system, juxtaposition of two numbers (usually) implies place value.
In algebra, juxtaposition of two variables implies multiplication.
In geometry, juxtaposition of the names of points represents lines or line segments.