Aspiration pneumonia (AP) is a sub-type of community-acquired pneumonia (CAP) still poorly recognized especially in the absence of an aspiration event. A further difficulty is the differentiation between AP and aspiration pneumonitis. From a clinical perspective, AP is becoming increasingly relevant as a potential cause of severe and life-threatening respiratory infection among frail and very old patients, particularly among those with CAP requiring inpatient care. Moreover, AP is frequently underdiagnosed and a clear-cut definition of this pathological entity is lacking. There are different factors that increase the risk for aspiration, but other common factors influencing oral colonization such as malnutrition, smoking, poor oral hygiene or dry mouth, are also important in the pathogenesis of AP and should be considered. While there is no doubt in the diagnosis of AP in cases of a recent witnessed aspiration of oropharyngeal or gastric content, we here proposed a definition of AP that also includes silent unobserved aspirations. For this reason, the presence of one or more risk factors of oropharyngeal aspiration is required together with one or more risk factors for oral bacterial colonization. This proposed definition based on expert opinion not only unifies the diagnostic criteria of AP, but also provides the possibility to devise easily applicable strategies to prevent oral colonization.