What does S and A stand for in a chart?

I'll paste an example. The z's are obviously degree orbs that can't translate properly from Word.

Aspects to Pluto

Pluto Trine Moon (1z57' S)
Your feelings are deep and intense, and frequently complicated. The dynamics of your family life and individual relationships are intricate and occasionally challenging. However, you have acute instincts and can usually sense emerging difficulties in associations and deal with them before they become unmanageable. You can become obsessed with particular objectives and will concentrate your emotional energy into attaining their realization.


Pluto Conjunct Mercury (5z21' A)
You have the power to be a dynamic and persuasive communicator. Perceptive and observant, you possess psychological insight into the motivations of others and even seem to sense what they are thinking. Whether or not you can read other people's thoughts isn't important, others tend to assume you can. You are keenly aware and able to assess situations quickly and accurately. Your intellect is sharp and penetrating, which gives you the ability to get to the bottom of anything; for this reason you are well-suited to investigative and research work. Alternatively, your relations with others will be strained if you come across as overbearing or intellectually superior. You can be cynical, extreme in your thinking, unable to compromise and disinclined to take any prisoners when arguing your case.

After the degree and minutes, every aspect ends with S or A. What do these stand for, what do these mean? I've wondered for the longest time.
 
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