A citrus juicer is used for squeezing juice from soft-centered, citrus fruits (e.g. orange, lemon, lime, grapefruit, etc). In its simplest form, it has a conical and ridged central part with a low circular bowl around it to catch the juice. The user centres the fruit and then presses and twists it over this auger. Going slightly more up-market, it may also have a lever-operated cup (operated hand) which is forced down from above on the 'back' of the fruit. There is usually no twisting action to this type, relying more on downwards pressure. In both types, pulp and seeds are retained by a circle of upright protusions which are placed before the juice reaches the collecting part of the bowl. The used halves of fruit are thrown away, composted or can be used to flavour jams, preserves, punches or similar.
A hand-held kitchen utensil version is known as a "lemon reamer", "citrus reamer," or simply a "reamer." Electric versions also exist.
Excellent citrus presses are the so-called Mexican Citrus Squeezers. I first saw them on Gino d'Acampo's TV series 'An Italian in Mexico' and after some research, found that they were being sold by branches of House of Fraser. They are so simple to use and really do extract as much juice as possible - more so than the citrus attachment on my food processor. The presses are marketed by a company in the USA and made in China. They come in three sizes - one each for oranges, lemons and limes.
A juice extractor is a machine that mechanically separates juice from the solid part (pulp) of most fruits, vegetables, leafy greens, and herbs. The pulp is usually discarded, but can also be used in muffins and breads or composted.
Most juice extractors are electric which obviously requires much less effort than their manual counterparts. A juicer differs from a blender in that it separates the juice from the pulp.
There are three main types of juicer: (1) centrifugal ones use blades and a sieve to separate juice from pulp; (2) masticating types that 'chew' fruit to a pulp before squeezing out the juice; and (3), triturating juicers that have twin gears to first crush fruit and then press it.
Masticating and triturating juicers can also produce juice from wheatgrass, unlike centrifugal juicers that cannot break down its fibres.
The single auger masticating juicer uses a profiled screw-style moulding to compact and crush fruit and vegetable matter against a static screen thus allowing juice to flow through the screen while pulp is expelled through a separate outlet.
Twin gear triturating machines are usually the most expensive juicers but offer the best juice yield. They employ two metal counter-rotating gears to crush organic vegetable/fruit material. The precise tolerance of the gears allows the juice to flow through the gap between them, while any large pulpy matter passes along the top of the gears and is discharged.
Having originally purchased a Breville JE4 electric juicer (pictured), primarily for extracting orange juice, I have to say it has long been superseded by the cheaper and more superior hand juicer (also shown). To extract citrus juice using the Braun juicer, the fruit has to be completely peeled and all pith removed before it can be juiced. This makes the whole thing a load of hassle and doesn't really save any time. The hand juicer just needs the fruit to be cut in half.