It's a conjunction used to introduce a contrasting idea or statement, similar to "but" or "yet" in English.
Here are some examples:
* Portuguese: "Ele é muito inteligente, no entanto, às vezes é muito distraído."
* English: "He is very intelligent, however, he is sometimes very distracted."
* Portuguese: "Eu queria ir à festa, no entanto, eu não me sentia bem."
* English: "I wanted to go to the party, however, I didn't feel well."