A professional tailor primarily alters clothing, such as hemming garments or making changes to a suit for a better personal fit. Many tailors also create fully custom clothing from a pattern or design. Tailors typically work with men's clothing, including suits, shirts, and coats, but may also work on women's garments.
A seamster or seamstress is a sewing professional who primarily makes clothes using a design or pattern. They also make alterations to clothing and repair garments. A seamstress works on all types of men's and women's clothing as well as non-clothing items like pillows and curtains.
Both seamstresses, seamsters, and tailors work in alteration shops, dry cleaners, and high-end fashion stores. In a men's suit store, you are more likely to work with a tailor. In a bridal boutique, you are likely to work with a seamstress.