The word Tajalli has many meanings. It is usually translated as manifestation, unveiling, or reflection. In this specific context, Tajalli refers to the various manifestations of Allah’s Divine Attributes and to the unveiling of their mysteries in the heart. Everything created is a sign of Allah, and if we look beyond the physical, we would see that everything in existence is connected to Him and there is nothing that is not dependent on Him. As such, all things in the universe are proof that He is our Creator and our Lord; they are manifestations or reflections of His Divine act of creation and are sustained by Him. Thus, they are all signs pointing to His presence.
Alternatively, Tajalli refers to the spiritual and mental experience in which a lover of God becomes acutely aware of this presence. All things, no doubt, are reflecting the Divine Attributes, but we rarely see them as signs. Oftentimes, we do not even look beyond the physical and it takes considerable mental effort to reflect upon this reality. However, there are occasions where a person becomes spiritually aware and is able to feel the presence of all things.
In such moments of high spiritual awareness and clarity, one is able to see that all things are indeed a sign of Allah, and so they get to see the Divine Attributes reflected in all things. Such a moment of high spiritual awareness can be long or short. It is called a state of Tajalli because in it the heart’s eye is able to see the Divine Attributes reflected in all things. In other words, it is a spiritual state in which the person experiences a sort of spiritual unveiling.