A consonant is a speech sound which obstructs the flow of air through the vocal tract. Some consonants do this a lot and some do it very little: the ones that make maximum obstruction ( ie plosives, which make a complete stoppage of air stream) are the most consonantal. Nasal consonants are less obstructive than plosives as they stop the air completely in the oral cavity but allow it to escape through the nasal cavity. Fricatives obstruct the air flow considerably, causing friction, but do not involve total closure. Laterals obstruct the air flow only in the centre of the mouth, no the sides, so the obstruction is slight. Some other sounds, classed as approximants, obstruct the air flow so little that they could almost be classed as vowels if they were in a different context ( eg /w/ or /j/).
There are 24 consonants in standard southern British English. They are plotted on the chart in Table 1 below.