Laitance and efflorescence are really two completely different things, but they are both white, powdery substances, which can be confusing.
In short, laitance is formed when there’s too much water in the concrete mix, while efflorescence is the deposit on masonry surfaces caused by soluble salts in the units or in the mortar.
Laitance can be avoided by controlling the amount of water in the concrete mix. Efflorescence can be prevented, or at least minimized, by selecting materials free of harmful salts and by preventing water from penetrating the masonry. This may be accomplished by the use of solid and tight mortar joints, capped walls, effective flashing, and adequate weather protection of the masonry during construction.
Both laitance and efflorescence can present both cosmetic AND structural problems.
Air entrainment is the intentional creation of tiny air bubbles in concrete. The bubbles are introduced into the concrete by the addition to the mix of an air entraining agent, a surfactant (surface-active substance, a type of chemical that includes detergents). The air bubbles are created during mixing of the plastic (flowable, not hardened) concrete, and most of them survive to be part of the hardened concrete. The primary purpose of air entrainment is to increase the durability of the hardened concrete, especially in climates subject to freeze-thaw; the secondary purpose is to increase workability of the concrete while in a plastic state.