Bacterial efflux describes a process where molecules are pumped from inside bacterial cells to outside. This is done by molecular machines called efflux pumps. These are found in the membrane of bacterial cells and they are very important because they contribute to antimicrobial resistance.
Many antibiotics work by getting inside bacterial cells where they interact with a specific target. Efflux pumps are able to physically pump those antibiotic molecules back out of the cell again which keeps the intracellular concentration below toxic levels meaning bacteria can survive at higher concentrations of the drug.