In DMDX there are specific terms that refer to unique DMDX things, I'll attempt to enumerate them here.
Run. When DMDX is told to execute a script we refer to it as running an item file.
Item File. An item file is a file that contains the script DMDX is going to follow
and it is a Rich Text File (so it has a .RTF file extension). It consists of two things, parameters and items.
Parameter. In the first section of an item file parameters are listed. In old item files the parameters were limited to the first line of the item file, nowadays an extended parameter line is possible. Parameters are active for the entire run.
Item. An item is one display sequence normally one reaction from a subject. Items occur following the parameters in an item file. The only unique thing differentiating one item from the next is the semi-colon at an item's end. Semi-colons are only usable as item delimiters, they can never be displayed or used for anything else. An item usually consists of a
correct response indicator, an item number and a series of frames, if not
it's just one frame.
Correct Response indicator or CR indicator.
Indicates which response within an item is the correct one.
Item number. Items have numbers both to identify the
response in the output file and also to indicate the item type
(instructions that don't gather RTs for instance have an item number of
Frame. A frame in an item is one display element. Normally frames are presented in a timewise sequence however they can be presented simultaneously. A frame can contain switches and an optional text segment. Frames are delimited by forward slashes (/)
Switches. Switches are normally only active for that frame as distinct from parameters that are active for the whole item file -- however there are switches that are also parameters depending on whether they are used in a frame or the parameter line.
Text segment. A text segment occurs between double quotes in a frame of an item. There can only be one text segment in a frame. A text segment can also be used as a file name if certain switches are present in an item.