On Shavuot, we commemorate the giving/receiving of Torah on Mt. Sinai.

Some of us customarily eat dairy.chal equals 40.2

There are many explanations for this.

One is that the Hebrew word for “milk” is “chalav” — chet/lamed/bet — and that the gematria (numerical value of the letters) equals 40, which is the same as the number of days that Mosheh spent on Sinai receiving Torah.

More on “40” from aish.com: [1]

“The number 40 has great significance throughout the Torah and the Talmud. The number 40 represents transition or change; the concept of renewal; a new beginning. The number 40 has the power to lift a spiritual state. Consider:

When a person becomes ritually impure, he must immerse in a ritual bath, a mikveh. The Talmud tells us that a mikveh must be filled with 40 se’ahs (a measure of water). Immersion in a mikveh is the consummate Jewish symbol of spiritual renewal.

It is no accident that in the story of Noah, the rain poured for 40 days, and submerged the world in water. Just as a person leaves a mikveh pure, so too when the waters of the flood subsided, the world was purified from the licentiousness which had corrupted it in the days of Noah.

Moses was on Mt. Sinai for 40 days and came down with the stone tablets. The Jews arrived at Mt. Sinai as a nation of Egyptian slaves, but after 40 days they were transformed into God’s nation.

According to the Talmud, it takes 40 days for an embryo to be formed in its mother’s womb.

In Kabbalah, 40 represents the four sides of the world, each side containing the ten Sefirot (esoteric powers).

When a rabbinical court finds someone guilty of a crime, the punishment is sometimes lashes, prescribed in the Torah as “forty less one.” The purpose is to bring the offender to a point of change, transition and atonement.

There are 40 days between the first day of Elul, when we begin to blow the Shofar to prepare for Rosh Hashana, until Yom Kippur, the end of the annual teshuva (repentance) period. These 40 days are the most auspicious time for personal growth and renewal.

According to the Talmud [2],  at age 40 a person transitions from one level of wisdom to the next.
After Moses led the Jewish people for 40 years in the wilderness,  he told them:
“God has not given you a heart to know, and eyes to see, and ears to hear, until 
this day.” [3]  
From here we see that it took the Jewish people 40 years before reaching a full level of understanding.”

But I think it’s enough to interpret “40” simply as a reminder of Mosheh’s 40 days on Mt. Sinai.

[1] http://www.aish.com/atr/The_Number_40.html
[2] Avot 5:26
[3] Dvarim/Deut. 29:3-4