Plasma is one of the four fundamental states of matter (the others being solid, liquid, and gas). Heating a gas may ionize its molecules or atoms (reducing or increasing the number of electrons in them), thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions.

Water polo, or water ball, is a team water sport. The playing team consists of six field players and one goalkeeper. The winner of the game is the team that scores the most goals. Game play involves swimming, treading water (using a sort of kicking motion known as "eggbeater kick"), players passing the ball while being defended by opponents, and scoring by throwing the ball into a net defended by a goalie. "Man-up" (or "power play") situations occur frequently. Water polo, therefore, has strong similarities to the land-based game of team handball.

A perennial stream or perennial river is a stream or river (channel) that has continuous flow in parts of its stream bed all year round during years of normal rainfall. "Perennial" streams are contrasted with "intermittent" streams which normally cease flowing for weeks or months each year, and with "ephemeral" channels that flow only for hours or days following rainfall.

Reserve Deputy Probation Officers are deputized volunteers who have received special training in order to assist Probation staff in a wide range of supervised responsibilities, that include direct involvement with juvenile an d adult probationers. Reserve Deputies are highly motivated, skilled, and caring people who want to serve their community as a part of the Los Angeles County Probation Department. Reserve Deputies are not a replacement for or an alternative to paid staff, but are intended to be an enhancement to existing resources.

The Doppler effect (or Doppler shift), named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague, is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.