Darts – Folds sewn into fabric expressly used to enhance the wearer’s shape. Commonly found in women’s blouses and dresses

Hems – Refers to the edge of a piece of fabric that needs to be sewn to prevent it from unraveling.

Seam: The line where two pieces of fabric are sewn together.

Seam Allowance: The space of fabric between the edge and seam. The seam allowance may be different depending on the type of fabric yo use.

Darts: A wedge-shaped fold used to shape patterns in order to make a garment fit better.

bias of the fabric is the diagonal line between the horizontal and vertical grain lines explained above.  And by diagonal, I mean a 45 degree slice between those lines.

Notches are small snip make on fabrics for references and it can also be use on curve area  to turn it inside out for a perfect finish

Notches are small small cuts like this
Okay, bias is like one wants to cut/make a flare skirt?
Yes Right. The fold of flare is also call bias.

Please can you help clarify what underarm measurement mean this is as regard sleeve

I don't understand d work of armhole
It's your armpit cut.
It's for geting armhole measurement incase you don't want to calculate it or if you don't want to use Standard one

What is the standard one

9 inches for bust 36 and above
And 7 for 34 downward
4-5 for age 4-7years
Most especially for fat people
They would not be able to raise their hands after sewing, if not up to d standard as given above.

Minimum armhole for a fat person is 9, you can take the underarm measurement for them.
[0It ranges between 9-12 for the fat people
What about for slim person of armhole
You can use between 7-9 depends on bust

The horizontal u mention is it on the tape rule
Is a measurement around the circumference of the body e.g when you take measurement around your bust/breast