Miriad uses the term `dataset' to refer to an image, a cube or a set of visibility data. A Miriad dataset is made from a host-system directory, i.e., the host operating system sees a `directory' whenever Miriad sees a `dataset'.
The task prthd provides an astronomical summary of a dataset. For visibility datasets, it will tell you the number of visibilities, the number of spectral-channels, the number of spectral-windows (IFs), the polarisations present and some information about frequencies. Note that if the visibility dataset contains multiple source or frequencies, it will only give you information about the source and frequency of the first record. For images, prthd will give dimension and axis information, minimum and maximum, etc. The input to prthd is the dataset name via the keyword in.