what you see in the painting is the subject matter of that painting. it is the totality of the picture/ the picture in totality or the focus of the picture.
eg. if a painting is showing a dingy room full of people in tatters, eating their meal, you could say the subject matter was Poverty.
however, a lot depends on the interpretation of the viewer. a person may feel that the focus is on eating hence the subject matter is mealtime....
many artists paint a series of paintings based on some specific/broad subject. that gives another indication about the true intent of the artist & subject matter of painting.

then the genre also helps decide the subject matter. still life, portraits, fantasy, surrealism, land & seascapes, etc. ...
the technique can also contribute - charcoal sketches, oils, waters, .....
hope this helps
all the very best

Subject matter is what the painting is of...
A portrait would be described as " the subject matter is a young girl" for instance.
Landscape, would be the subject matter of an outdoor scene, woods, mountains, etc.

If you already have oil paints, brushes/medium(s) and canvases or panels, please bring them to the first

class. We will talk about a well-rounded palette and personal choices. It is a good idea to start with a
very basic set of supplies and add as you find appropriate to your artistic needs.
A selection of oil paints of various colors:
Selection of oil paints with at least one cool and one warm version of red, blue, yellow, green, and
single tubes of burnt sienna, burnt umber, black and white. Suggested palette: Titanium White (larger
tube), hansa yellow, lemon yellow, naples yellow, scarlet lake, alizarin crimson, ultramarine blue, cobalt
blue, cerulean blue, burnt sienna, burn umber, raw umber, lamp black. You may choose to start with
paints you already have and add colors after our first class meeting.
Turpenoid
Turpenoid is lower odor and much safer than turpentine
Linseed oil – small bottle, optional (can be used to make various painting mediums)
Palette or disposable palette sheets
Bristle Brushes
You will want a small selection of oil painting brushes in the following (or similar) sizes:
Size 0, 1, 4 rounds
Size 2, 4, 6 flats
1 or 2 filberts
Double palette cups or a couple of small glass jars with lids (if possible).
Baby food jars or bacon bits jars are great. Example: double palette cup (no lid)
5 canvas boards or canvases
Your choice of sizes between 8” x 10” and 11” x 14”
Optional but very useful
Table easel (from hobby stores or art stores from $15 to $50.)
Rags or paper towels
Lots of them!!