[θ] is voiceless, strong (fortis), constrictive fricative, forelingual, interdental (articulated by the blade of the tongue against the upper incisors. It is a fricative because you produce it by squeezing the breath stream between your tongue and teeth. It differs from a dental consonant in that the tip of the tongue is placed between the upper and lower front teeth, and therefore may articulate with both the upper and lower incisors, while a dental consonant is articulated with the tongue against the back of the upper incisors.