complex sentence
complex sentence (oración compleja)
a sentence made of one independent clause and at least one dependent clause, often joined by because, although or when.
Example
Although the plan is costly, it will save lives. (Although the plan is costly cannot stand alone.)
In Spanish
complex sentence (oración compleja) — una oración formada por una cláusula independiente y al menos una cláusula dependiente, a menudo unidas con because, although o when.
Although the plan is costly, it will save lives. (Although the plan is costly no puede estar sola.)