Copo vs. taça
While both copo and taça can refer to vessels used for drinking, the distinction depends heavily on the shape of the object and the region (Brazil vs. Portugal). Generally, copo is a standard everyday glass with a flat bottom, whereas taça implies either a stemmed glass or a bowl shape.
Copo
A1This word refers to a standard cylindrical vessel without a stem or handle, sitting flat on the table. It is used universally for water, juice, and soda. However, a crucial regional difference is that in Portugal, a wine glass is usually called a copo, whereas in Brazil, using copo for wine suggests a cheap, stemless tumbler.
Eu bebo um copo de água todas as manhãs.
(I drink a glass of water every morning.)
Por favor, traga um copo limpo para o suco.
(Please bring a clean glass for the juice.)
Em Portugal, é comum pedir um copo de vinho tinto.
(In Portugal, it is common to order a glass of red wine.)
Vamos beber um copo depois do trabalho?
(Shall we go for a drink after work? (Common European Portuguese expression))
Taça
A2In Brazil, this word primarily refers to a drinking glass with a stem and a foot (stemware), used specifically for wine and champagne. In Portugal, taça typically refers to a bowl used for eating (like soup, cereal, or dessert) or purely for champagne, but rarely for regular wine.
O garçom serviu o vinho em uma taça de cristal.
(The waiter served the wine in a crystal glass. (Brazilian usage implying stemware))
Comi uma taça de cereais ao café da manhã.
(I ate a bowl of cereal for breakfast. (European Portuguese usage))
Erguemos a taça para fazer um brinde com champanhe.
(We raised the glass to make a toast with champagne.)
Ela pediu uma taça de sorvete de sobremesa.
(She ordered a bowl of ice cream for dessert.)
Summary
Use copo for everyday flat-bottomed glasses (water, juice). Use taça in Brazil for wine glasses (stemware), but use copo in Portugal for wine. Remember that in Portugal, taça often means a bowl for food.