They say a picture is worth a thousand words...
The target has undergone complete image collapse.
As the process is normally depicted: the core, upon its destruction, first swells up and ruptures, followed rapidly by the extensive swelling and rupture of the Angel's remaining body. This is usually so explosive that all of the red fluid is thrown into the air and gradually falls as a "rain of blood", eventually accumulating into a massive pool of fluid.
The Fifth Angel, while undergoing prompt and violent image collapse, leaves its whip extensions behind intact. It's not known if they eventually deteriorate as well, or if they are, for some reason, not treated as a part of the Angel's body. If the latter is the case, this is perhaps analogous to the silk of a spider (which, in some species, is actively wielded as a weapon!), which originates from the spider's body but would no longer be considered part of it.
In the case of the 6th Angel, only the core and drill extension burst immediately, with the rest of the body, instead of exploding, pouring down fluid from multiple points of rupture, and, upon being reduced to little more than a shell, collapsing into its own pool of "blood". Given how gradual this Angel's collapse is, the shell presumably continues to dissolve off-screen.
Image collapse also occurs with Lilith in Evangelion 3.0: You Can (Not) Redo once the two Spears of Longinus are removed by Eva-13. Unlike all other known cases of the phenomenon, Lilith has no explicit core, but was evidently killed in offscreen events by unknown means, as Kaworu refers to the body as a corpse. The Spears appear to have been stabilizing Lilith's form, evidenced by the fact that the body along with its disembodied head swell and burst immediately after the Spears are withdrawn.
The blood-colored fluid is never explicitly identified in the dialogue. However, the script for Evangelion 3.0 indicates that, at least in the case of Lilith, it is indeed LCL. Because there is no discernible difference in the fluid that Lilith reduces to, and that comprising the bodies of the Third through Twelfth Angels, it is probably LCL in all instances.
Why would an Angel's A.T. Field collapse upon the destruction of its core? The reason may be implied through a computer display indicating that Eva-01's A.T. Field originates from both its core unit and the entry plug, which interface directly to achieve synchronization. The entry plug is referred to in Explanation of Evangelion 1.01 as the "throne for a soul", referring to the soul of the pilot. Since an Angel does not require an entry plug to generate an A.T. Field, the source must therefore be its core alone. It is probably the case that, as in the original Evangelion series, the Angel's core houses its soul, and the A.T. Field manifests from the soul. When the core is destroyed, the soul may be either liberated from it or destroyed outright, and with nothing remaining to generate an A.T. Field, the field collapses.
The image collapse phenomenon appears to be present, however unnamed, in the original Evangelion series, wherein a sufficient disruption to a person's A.T. Field -- such as the uncontrolled manifestation of destrudo or interference from an Anti A.T. Field -- resulted in the destruction of one's body. In the cases of Rei Ayanami and Lilith's Third Impact form, this is depicted as the body spontaneously falling apart into multiple chunks, which remain intact after the initial "destrudo release" (i.e., do not continue to reduce into smaller and smaller pieces). Lilin, alternatively, burst into orange LCL, a typically explosive process. Adam's Children and Evangelions are never seen undergoing a similar phenomenon, remaining physically intact in the presence of an Anti A.T. Field, after their cores are destroyed, or both. Neither the Rei or Lilin variations of image collapse have been seen in the New Theatrical films, though a form of the latter may be implied to have happened to Shinji at the end of Evangelion 2.0: You Can (Not) Advance.
Notes & References
- The official translation provided by Dan Kanemitsu for khara's official film festival subtitles is unknown. "Image collapse" is an educated guess made by editor Reichu. "Image", here, is in the sense of a shape or form. The implied link to "self-image" is intended.
- Despite a single mention, the term has been adopted by the Japanese fan community, presumably on account of its usefulness.
- 「目標は完全に形象崩壊しました。」 Evangelion 1.11: You Are (Not) Alone. Translation by Reichu.
- Evangelion 3.33 Blu-Ray: Script. Translations by Reichu.
C1241: Lilith rupturing. Swells under pressure and abruptly pops!
C1242: Same camera placement. Giant Ayanami (Gendo in foreground) inflates with a whoosh and explodes from the inside.
C1243: Gendo basking in L.C.L. downpour, high angle view.
C1245: Mk.06 (Eva-13 in foreground) floating above the L.C.L. lake.