A comminute is effectively a puree made from whole citrus fruit. Unlike most juices and purees, which are made from whole fruit, citrus juices are generally produced from just the endocarp (the fleshy parts one would normally eat) and do not include any of the outer layers of the fruit. The juices, and in some cases also some of the "cells" (juice vesicles) of which the edible parts are comprised, are extracted such that the rest of the fruit is left behind.
However, in a comminute these parts are intentionally included, generally by mechanically processing them to a pulp-like consistency and incorporating with all the juices from the fruit. The product is sieved or filtered to remove any seeds and may then be processed as with any other fruit puree. The inclusion of these extra parts of the fruit gives the comminute a distinct flavour that differs from the standard juice.
Infusions are used as a means of capturing the flavour of ingredients that do not readily lend themselves to inclusion in recipes in their natural form. Generally, a solvent is used to draw the flavour out of a solid item so that the flavour can then be used in liquid form. The liquids used for this vary, but include water, sugar solutions and alcohols.
A good example of a product used in infusion form is Elderflower, which is popular in various soft drinks, cordials and other foodstuffs. Elderflowers do not readily lend themselves to direct addition to recipes as it is unappealing to have bits of flowers floating in liquid products, and in this form the flavour would not readily disperse evenly throughout the whole product. They also have limited liquid content that could be extracted by pressing or squeezing as one would generally do with a fruit. Elderflower infusions are therefore produced by soaking the flowers in, for example, a sugar solution. This draws the natural flavouring compounds out of the flowers, which may then be sieved out to leave a liquid with the characteristic flavour and aroma of Elderflowers. This can then be used in a similar manner to a more standard fruit juice concentrate.