An inseam is the seam along the inner length of pants. In men’s trousers, the sizes are waist measurement first then the inseam length. For instance 28 x 36. This is a very important measurement when making pants.
Interfacing is used to give stability to the fabric. It can be fusible or sew in. There are many different weights of interfacing so that the weight stabilizes the specific parts of clothing. Like collars, cuffs, buttonhole areas, etc. Interfacing is also used when making quilts. Machine appliqué requires the use of interfacing to keep the applique stable for the machine stitching. This is used for unfinished edged appliqué.
Irons are used when sewing. The fabric is washed before being used in quilting, so it must be ironed before cutting so that you get a nice even edge on your fabric.