FEV, or Forced Expiratory Volume, is a measure that tells us how much air a person can forcefully exhale in one second after taking a deep breath. There are some synonyms for the term "FEV" that are often used interchangeably, including Forced Vital Capacity (FVC), Forced Expiratory Flow (FEF), and Peak Expiratory Flow Rate (PEFR). FVC refers to the maximum amount of air a person can exhale after taking a deep breath, whereas FEF represents the rate of air flow during the middle portion of a forced exhalation. PEFR is a measure of the maximum airflow that can be achieved during a forceful exhalation and can be used to monitor conditions such as asthma or COPD.