Grupo vs. conjunto
While both grupo and conjunto can be translated as "group" in English, they are not always interchangeable. The main difference lies in the nature of the collection they describe: grupo is a general term, while conjunto implies a cohesive and unified whole.
Grupo
A1This is the most common and versatile word for "group". It refers to a number of people, animals, or things that are together in the same place or have a common characteristic, without necessarily forming a single, functional unit. It is the general, all-purpose term.
Un grupo de turistas esperaba el autobús.
(A group of tourists was waiting for the bus.)
Me uní a un grupo de lectura para conocer gente nueva.
(I joined a reading group to meet new people.)
Mi banda favorita es un grupo de rock de los años 80.
(My favorite band is a rock group from the 80s.)
Sobre la mesa había un pequeño grupo de llaves olvidadas.
(There was a small group of forgotten keys on the table.)
El profesor dividió la clase en varios grupos de trabajo.
(The teacher divided the class into several work groups.)
Vimos un grupo de ciervos en el bosque.
(We saw a group of deer in the forest.)
Conjunto
B1This word implies a "set" or a collection of elements that are meant to be together, work together, or are seen as a single, complete unit. The items in a conjunto have a strong relationship with each other and are often interdependent to form a whole.
Compró un elegante conjunto de falda y chaqueta.
(She bought an elegant skirt and jacket set (outfit).)
Este conjunto de herramientas incluye todo lo necesario para la reparación.
(This tool set includes everything needed for the repair.)
La urbanización es un conjunto de edificios con áreas comunes.
(The development is a complex (or set) of buildings with common areas.)
En matemáticas, un número primo es un elemento del conjunto de los números enteros.
(In mathematics, a prime number is an element of the set of whole numbers.)
Hay que analizar el problema en su conjunto, no por partes.
(One must analyze the problem as a whole, not in parts.)
El conjunto de música folclórica dio un concierto maravilloso.
(The folk music ensemble gave a wonderful concert.)
Summary
In short, use grupo as your default, general word for any collection of people or things. Use conjunto when you want to emphasize that the elements form a cohesive, complete, or functional unit, like an outfit (conjunto de ropa), a set of items (conjunto de herramientas), a housing complex (conjunto residencial), or when considering something as a whole (en su conjunto).