The symbols $\{$, $\}$, $($, and $)$ are covered in Section b.5: Brackets. The symbols $\mathcal{L}$, $\mathcal{N}$, $\mathfrak{R}$, and $\mathfrak{I}$ are covered in Section b.1: Font. See also Section b.8: The Greek Alphabet.

A comma can be used in numbers to group by thousands, e.g. $5,\!316,\!522$. In some parts of the world, the comma is used like a decimal point.

Commas are used to mean ‘or’ in a list of possible values, e.g. ‘$x=1,2$’ means $x=1$ or $x=2$ (see Section 7.5.4: Multiple Solutions). They are similarly used in lists of set elements (Section 8.1: Sets), e.g. $\{1,2,3,\ldots\}$ is the set of natural numbers.

Commas are also used to separate coordinates of a point or vector (Section 11.1: Cartesian Coordinates), e.g. $(3,-1)$ is the point with an $x$-coordinate of $3$ and a $y$-coordinate of $-1$.

The symbol $\cup$ indicates set union, and $\cap$ indicates set intersection (Section 8.1.1: Unions and Intersections).

The symbol $\in$ means ‘is a member of’ or ‘is in’. The symbol $\notin$ means ‘is not a member of’ or ‘is not in’. The symbol $\ni$ means ‘contains’. See Section 8.1: Sets.

$\subset$, $\supset$, $\subseteq$, and $\supseteq$

These symbols mean ‘is a proper subset of’, ‘is a proper superset of’, ‘is a subset of’, and ‘is a superset of’, respectively (Section 8.1.2: Subsets and Supersets).

This symbol means ‘is proportional to’. See Section 4.2.1: Proportion and Question 9.1.1.

These symbols mean ‘is approximately equal to’.

This symbol is often referred to as ‘twiddle’ by mathematicians, but most people would call it a ‘tilde’.

Like the symbol $\equiv$, twiddle often represents an equivalence relation, and $a\sim b$ is pronounced ‘a twiddles b’. In particular, it can indicate geometric similarity (Section 10.6.5: Congruence and Similarity).

It can mean ‘is distributed as’ in statistics.

This symbol can be used to show that two things are approximately the same in some way; it could mean they are of the same order of magnitude, or are proportional by a dimensionless factor, or that two functions have asymptotic equality, or it could just mean the same as $\approx$ (especially when followed by $=$).

It can mean ‘not’ in logic (Section 9.1: Logic).

Above a variable, e.g. $\tilde x$, it’s used similarly to $\hat x$ or $x’$: as a way to create a new symbol related to $x$ in some way. For example, $\tilde f$ may be the Fourier transform of $f$, and in statistics $\tilde x$ may be the median of $x$ (Section 6.2.1: Averages).

This is the symbol for integration (Section 15.4: Integration).

The partial derivative of $y$ with respect to $x$ would be written as $\frac{\partial y}{\partial x}$.

This is the hebrew letter ‘aleph’, which is used for a kind of infinity in set theory (Question 9.6.4).

This is the symbol for infinity.

This is the symbol for dollars (Section 2.1.2: Money).