This is the process of developing a film for a (very) long time, e.g. 30-240 minutes, with little or no agitation. The aim is to use compensation to bring up shadow detail in what would otherwise be a high-contrast image without producing extreme highlight density.
In other words, it is a method for reducing the total dynamic range of an image without (in theory) reducing highlight contrast.
Classic zone system "Contraction" or "N-" development reduces the overall dynamic range by reducing contrast in the image, resulting in a flatter look. Semi-stand however aims to reduce the dynamic range in the shadows without unduly affecting highlight contrast, the aim is to produce the contraction effect without making the highlights flatter.
The developer of choice for this technique is typically highly-diluted Rodinal, e.g. at 1+100 or even 1+200.
The term "semi-stand" usually refers to techniques where there might be 30-60s of initial agitation followed by agitation at 3-5 minute intervals; this frequent agitation limits the total development time to about 20-30 minutes depending on the film. It has practically no risk of bromide drag and therefore is a (relatively) safe place to start experimenting.
The term "stand" usually refers to techniques where initial agitation of 30-60s is performed, followed by an inversion or two after a few minutes and then absolutely no inversions for the remaining development time, which will be on the order of an hour or more.
This approach risks bromide drag with some films but offers the greatest shadow detail.
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