By definition, a phoneme is a consonant if air flow is restricted in some way. The format for Articulatory Analysis of consonants involves three main things: passive place of articulation, manner of articulation, and active place of articulation. The place of articulation(both passive and active) refers to which articulator(s) are being used. Most, but not all consonants have both a passive place and an active place.
The passive place of articulation is the articulator that does not move. Teeth, the uvula, the epiglottis, the alveolar ridge, and the radical are just a few of the articulators that will always be passive. They cannot change their position. Articulators that can change position can be either passive or active. The lips are a good example of a mobile articulator that is often passive. Sometimes one is passive while the other is active.
The weird thing about the passive place of articulation is that it isn’t always literally stationary. Meaning that depending on the sound and how it is being pronounced in this particular instant, sometimes the passive place of articulation has to move. The best example I know of for this, is a sound produced in the Punjabi language where the speaker must curl the tip of the tongue to touch the sub-apical to the upper labial(lip). The sub-apical is the active place of articulation and the upper-labial is considered passive; however, in order to make the contact, the user must purse the upper lip, pulling it down and around the upper teeth. The upper lip moves even though it is passive.
Active Place of Articulation
As you probably know or guessed, the active place of articulation is the articulator that moves to make some sort of contact with the passive place. There are no articulators that are always active. Usually, if one simply describing a phoneme the traditional way, the active place of articulation is omitted. For instance, one might talk about a “sonorant alveolar fricative”. That’s all fine and dandy, except that I can think of five different phonemes off the top of my head that could fit that description. However, if you called it a “sonorant apical to alveolar fricative” then we have narrowed it down quite a bit.
Despite the fact that the active place is often omitted in description, there are some phonemes that only have an active place but no passive place. The sonorant epiglottal trill as found in the Semitic languages is one of these. In short, the active place of articulation is very important in linguistics.