Any aspect that is not a major aspect, i.e. all aspects apart from the conjunction, opposition, square, trine and sextile. When interpreting a chart, the minor aspects are considered to be of secondary importance to the major aspects.
The minor aspects are:
Semi-Sextile (30 degrees)
Quincunx (150 degrees)
Quintile (72 degrees)
Bi-Quintile (144 degrees)
Semi-Square (45 degrees)
Sesqui-Square (135 degrees)
Semi-Quintile (36 degrees)
Septile (51 degrees 26 minutes)
Nonile (40 degrees)
The following aspects are rarely used:
Semi-Octile (22.5 degrees)
Squile (75 degrees)
Squine (105 degrees)
Tri-Decile (108 degrees)
Quindecile (165 degrees)
Asto.com
https://www.astrology42.com/aspects/2Minor Aspects
These aspects refer to the following:
Semi-Sextile (30 degrees)
Quincunx or Inconjunct (150 degrees)
The first 2 of the minor aspects have a heavier weight than the other minor aspects because they are divisible by 30 degrees (like the major aspects) thus having an impact on the elements involved in the chart.
The rest of the minor aspects are as follows (and are often not used):
Quintile (72 degrees)
Biquintile (144 degrees)
Septile (144 degrees)
Semi-Square (45 degrees)
Sesquisquare (135 degrees)
Novile (40 degrees)
3Hard Aspects: Challenging & Dynamic
Hard Aspects relate to the Square (90°), Opposition (180°), Quincunx (150°) and some of the Conjunctions (0°) and Semi-sextiles (30°), depending on the planets and the harmony of planets/signs involved.
4Easy Aspects: Harmonious & Flowing
Easy Aspects refer to the Trine (120°), Sextile (60°), and some of the Conjunctions (0°) and Semi-sextiles (30°), depending on the planets and the harmony of planets/signs involved.
It is my understanding that the most popular Minor aspects are; the Inconjunct or Quincunx, the Semi-Sextile, the Semi-Square and the Sesquiquadrat.
https://www.universalsky.com/minor-aspects-in-astrology/