For integer subscripts, the natural numeric order: 0, 1, 2, 3, …​ For strings, the ASCII collating sequence.

The ^ character (ASCII 94). Prefixes global variable names.

The I/O device to which READ and WRITE are directed. Identified by $IO. Changed by USE.

An integer (0, 1, 10, or 11) associated with each node in the variable tree, returned by $DATA. Encodes whether the node has a defined value (units digit) and whether it has descendants (tens digit).

A specification of a line in a routine, used by DO, GOTO, and $TEXT. May include a label, an offset, and a routine name.

A variable whose name begins with ^. Stored persistently on disk, shared among all processes, and organized as a hierarchical tree.

A name or integer literal at the beginning of a line that identifies the line for reference by DO, GOTO, or $TEXT.

In the 1976 standard, a dot-based notation (not used in NBS 118 but present in some implementations) to indicate block structure.

A variable without the ^ prefix. Exists only in the current process’s memory; lost when the process terminates.

A hidden register that remembers the global name and all but the last subscript of the most recently executed global reference. Used to interpret naked references of the form ^(subscript).

A global variable reference of the form ^(expr[,…​]) that relies on the Naked Indicator for the global name and leading subscripts.

A point in the variable tree identified by a name and zero or more subscripts. Each node may have a value, descendants, both, or neither.

In the MUMPS system model, the execution context of a single process, containing local variables, the routine stack, the Test Switch, and the Naked Indicator.

A :tvexpr appended to a command word or (for DO, GOTO, XECUTE) an argument, which causes conditional execution without affecting $TEST.

The unit of program storage and interchange. Consists of a routine head (the routine name) followed by a routine body (a sequence of lines).

A stack that records return points for DO and XECUTE calls. QUIT pops the stack.

The remainder of the current line. FOR and IF control execution of everything to their right on the same line.

A read-only system variable prefixed with $ (e.g., $HOROLOG, $TEST). Provides access to system state.

A syntactic construct denoting a variable node: either a local variable name, a global variable name, or a naked reference, any of which may be subscripted.

The sole data type in MUMPS. All values, including numbers, are represented as character strings.

An expression enclosed in parentheses after a variable name, used to select a descendant node. Multiple subscripts, separated by commas, identify a path through the tree.

A Boolean register (0 or 1) whose content is available via $TEST. Set by IF (with arguments), and by OPEN, LOCK, and READ when a timeout is used.

A :numexpr appended to arguments of READ, OPEN, or LOCK, specifying a maximum wait time in seconds. Sets $TEST on completion.

0 (false) or 1 (true). The truth-value interpretation of any string is: take its numeric interpretation; if the result is 0, the truth value is 0; otherwise it is 1.