The chemistry term miscible refers to the property of various liquids that allows them to be mixed together. Substances are said to be immisicible if they cannot be mixed together, e.g oil and water.
In organic compounds, the length of the carbon chain often determines miscibility relative to members of the homologous series. For example, in the alcohols, ethanol has two carbon atoms and is miscible with water, whereas octanol has eight carbon atoms and is not miscible with water. Octanol's immiscibility leads it to be used as a standard for partition equilibria . This is also the case with lipids, the very lengthy carbon chains of lipids cause them to almost always be immiscible with water.
Miscibility can arise for a number of reasons. In the alcohol examples above, the group can form hydrogen bonds with water molecules. In aldehydes and ketones the hydrogen bond can form with a lone pair of electrons on the carbonyl oxygen atom.