Adaptation

Adaptation in biology refers to a heritable trait or characteristic that improves an organism's ability to survive and reproduce in a particular environment. It can also refer to the evolutionary process through which such beneficial traits arise in a population over time.

• An adaptation (trait) is genetic -- it's not something an individual organism consciously develops in response to the environment. Instead, individuals born with a beneficial trait tend to survive and have more offspring, spreading that trait.
• Adaptation (the process) happens via natural selection acting on variation: for example, in a cold climate, animals with thicker fur (a genetic trait) may survive better and leave more offspring, so thick fur becomes more common -- an adaptation to cold.
• Don't confuse adaptation with acclimatization: acclimatization is a temporary adjustment (like your body making more red blood cells at high altitude), whereas an adaptation is a long-term evolutionary change (high-altitude populations evolving greater lung capacity over generations).

• A question might give an example of a trait and ask why it exists -- e.g., "Polar bears have white fur because...?" The answer relates to adaptation: white fur camouflages them in snow, improving hunting success (thus it was favored by natural selection).
• Be prepared for scenarios where a population changes over generations to become better suited to environment pressures (classic adaptation story). For instance, insects evolving pesticide resistance: the resistant trait is an adaptation that spread because those insects survived to reproduce.
• Also watch for trick statements implying that organisms intentionally adapt out of need. The correct understanding: random mutations produced variation, and the environment "selected" those variants that were advantageous (nature doesn't give organisms what they need except via this selection process).