Cloud the bottom of the hierarchy. Clouds in the troposphere assume five physical forms based on structure and process of formation. These forms are commonly used for the purpose of satellite analysis. They are given below in approximate ascending order of instability or convective activity. "Non-convective" stratiform clouds appear in "stable" airmass conditions and, in general, have flat sheet-like structures that can form at any altitude in the troposphere. The stratiform group is divided by altitude range into the genera cirrostratus (high-level), altostratus (mid-level), stratus (low-level), and nimbostratus (multi-level). Fog is commonly considered a surface-based cloud layer. The fog may form
Trick-or-treating Trick-or-treating Trick-or-treating has become a Halloween ritual custom for children and adults in many countries. The term ""trick-or-treat"", most commonly associated with the USA, but with its cultural origins in the Celtic regions of Europe, is now found in use all over the world since the spread and establishment of now popular cultural activities, previously by means of colonialism and the spread of Christianity. Typically, children in costumes travel from house to house, asking for treats with the phrase "Trick or treat". The "treat" is usually some form of candy, although in some cultures money is used instead. The "trick"