Barra vs. haltere
The distinction between these two terms lies in the size of the equipment and how it is held. While barra specifically refers to the long bar (barbell) requiring two hands, haltere refers to the short handheld weight (dumbbell).
Barra
A2This word literally translates to bar. In the context of a gym, it refers to the long horizontal barbell used for heavy compound lifts like squats, deadlifts, and the bench press.
Você precisa colocar as presilhas na barra antes de começar.
(You need to put the clips on the barbell before starting.)
A barra olímpica pesa geralmente vinte quilos.
(The Olympic barbell usually weighs twenty kilos.)
Ele carregou a barra com muito peso para o agachamento.
(He loaded the barbell with a lot of weight for the squat.)
Não esqueça de limpar a barra depois de usar.
(Do not forget to wipe down the barbell after using it.)
Haltere
B2This word translates to dumbbell rather than barbell. It refers to the smaller, short-handled weights held individually in one hand for isolation exercises.
Prefiro fazer rosca direta com um haltere em cada mão.
(I prefer doing bicep curls with a dumbbell in each hand.)
Os halteres mais pesados ficam na parte de baixo do suporte.
(The heavier dumbbells are on the bottom part of the rack.)
Você pode me passar aquele haltere de dez quilos?
(Can you pass me that ten-kilo dumbbell?)
O treino de hoje utiliza apenas um par de halteres.
(Today's workout uses only a pair of dumbbells.)
Summary
Use barra when talking about the long bar requiring two hands (barbell), and haltere when talking about the small individual hand weights (dumbbells).