On a recent Shabbos afternoon, I saw a sign at a nusach Ashkenaz, 'Yeshivishe' minyan advertising a special shiur on the occasion of יומא דהילולא דקדישא של - מרן החזו"א זצוק"ל (sic).
A good illustration of the confusion that has afflicted some people recently.
They want to mark the yahrzeit of the Chazon Ish in a Litvishe way - by having a special shiur. A nice idea. But at the same time they use Hassidic terminology, by using the expression יומא דהילולא דקדישא (actually should really be, leshitasam, קדישא, not דקדישא) instead of the Litvishe/Ashkenaz expression of יאהרצייט. This is not a Hassidic minyan, nor was the Chazon Ish Hassidic. So why the Hassidic terminology?
And it is not merely an issue of different words that mean the same thing. There is a difference between the Ashkenaz/Litvish approach to a death-anniversary, called a yahrzeit, and the Hassidic one to the same occasion, which they refer to as hillulah, which the different terminology reflects.
The Ashkenaz conception is that yahrzeit is a solemn occasion, a time for introspection and fasting. As brought down in Shulchan Aruch, מנהג אשכנז is to fast on a יאהרצייט. By contrast, the conception of הילולא (wedding/celebration), used by Hassidim, is that the day is a holiday, a time for celebration. Therefore Hassidim make a festive meal and celebrate on their Rebbe's יאהרצייט. By contrast, Litvaks give a special shiur on the יאהרצייט of the ראש ישיבה, and they use the old Ashkenaz term of יאהרצייט.
Bottom line - הילולא and Litvish don't go together. Let's keep terms and traditions consistent.