B"H
It's known that every number has some significance in the Torah, what then does the number 800 (represented by a final fay according to one system of gematria) represent in the Torah, in other words what (other) significance does that number have?
Blessings and success
800 is the number of years Adam lived after the birth of Shet, as it is written:
וַיִּהְיוּ יְמֵי אָדָם אַחֲרֵי הוֹלִידוֹ אֶת שֵׁת שְׁמֹנֶה מֵאֹת שָׁנָה, וַיּוֹלֶד בָּנִים וּבָנוֹת
After the birth of Seth, Adam lived 800 years and begot sons and daughters. (Gen. 5:4)
800 is also the number Yered lived after Ḥanokh, as it is written:
וַיְחִי יֶרֶד אַחֲרֵי הוֹלִידוֹ אֶת חֲנוֹךְ שְׁמֹנֶה מֵאוֹת שָׁנָה, וַיּוֹלֶד בָּנִים וּבָנוֹת
After the birth of Enoch, Jared lived 800 years and begot sons and daughters. (Gen. 5:19)
800 is also the number of men that Adino, David's warrior, fought in one battle, as it is written:
אֵלֶּה שְׁמוֹת הַגִּבֹּרִים אֲשֶׁר לְדָוִד, יֹשֵׁב בַּשֶּׁבֶת תַּחְכְּמֹנִי רֹאשׁ הַשָּׁלִשִׁי הוּא עֲדִינוֹ (העצנו) הָעֶצְנִי עַל שְׁמֹנֶה מֵאוֹת חָלָל בְּפַעַם (אחד) אֶחָת
These are the names of David’s warriors: Josheb-basshebeth, a Tahchemonite, the chief officer—he is Adino the Eznite; [he wielded his spear] against eight hundred and slew them on one occasion. (II Sam. 23:8)
You can get some nice results by querying the following sites for 800 (or for any other number for that matter).
On Dicta, this will return all three instances (as mentioned in a previous answer) where an exact quantity of 800 is mentioned in Tanach: https://search.dicta.org.il/result?text=800
On (my very own) Base Hasefer, one can play with gematria searches on the word and on the pasuk level.
For a list of over 100 pesukim containing highlighted words with a gematria of 800: https://basehasefer.com/#/search?terms=800&format=G
For a summary listing of all those words in a Lexicon view showing distribution figures for how often each word occurs: https://basehasefer.com/#/lexicon?gematria=800 - results are below by order of descending number of occurrences (eg. קשת occurs 35 times):
For a list of over 300 pesukim containing highlighted words with an atbash of 800 (sum of the atbash value of each letter): https://basehasefer.com/#/search?terms=800&format=A
For a summary listing of all those words in a Lexicon view: https://basehasefer.com/#/lexicon?atbash=800
Additionally, here's an image of the results of an advanced search listing the three pesukim that have a total gematria of 800 (there are none with an atbash of exactly 800, but a few close ones)
And finally, if one wants to list the 17 times where the exact phrase "שמנה מאות" occurs in Tanach, allowing for prefixes and malei/chaseir, (regardless of whether those words are part of a larger numeric phrase not equal to 800) we go here: https://basehasefer.com/#/search?terms="שמנה%20מאת"&precision=2
There is a maaseh brought down in Mishnah Nedarim 9:5:
פּוֹתְחִין לָאָדָם בִּכְתֻבַּת אִשְׁתּוֹ. וּמַעֲשֶׂה בְאֶחָד שֶׁנָּדַר מֵאִשְׁתּוֹ הֲנָאָה וְהָיְתָה כְתֻבָּתָהּ אַרְבַּע מֵאוֹת דִּינָרִין, וּבָא לִפְנֵי רַבִּי עֲקִיבָא וְחִיְּבוֹ לִתֵּן לָהּ כְּתֻבָּתָהּ. אָמַר לוֹ, רַבִּי, שְׁמֹנֶה מֵאוֹת דִּינָרִין הִנִּיחַ אַבָּא, וְנָטַל אָחִי אַרְבַּע מֵאוֹת וַאֲנִי אַרְבַּע מֵאוֹת, לֹא דַיָּהּ שֶׁתִּטֹּל הִיא מָאתַיִם, וַאֲנִי מָאתָיִם. אָמַר לוֹ רַבִּי עֲקִיבָא, אֲפִלּוּ אַתָּה מוֹכֵר שְׂעַר רֹאשְׁךָ, אַתָּה נוֹתֵן לָהּ כְּתֻבָּתָהּ. אָמַר לוֹ, אִלּוּ הָיִיתִי יוֹדֵעַ שֶׁהוּא כֵן, לֹא הָיִיתִי נוֹדֵר, וְהִתִּירָהּ רַבִּי עֲקִיבָא
They release a vow by reference to a wife’s kesubah. And it once happened that a man vowed not to benefit from his wife and her kesubah amounted to four hundred denarii. He went before Rabbi Akiva, who ordered him to pay her the kesubah [in full]. He said to him, “Rabbi! My father left eight hundred denarii, of which my brother took four hundred and I took four hundred. Isn’t it enough that she should receive two hundred and I two hundred?” Rabbi Akiva replied: even if you have to sell the hair of your head you must pay her her kesubah. He said to him, “Had I known that it is so, I would not have vowed.” And Rabbi Akiva released his vow.
See Mishnah Yoma 3:7:
בַּשַּׁחַר הָיָה לוֹבֵשׁ פִּלּוּסִין שֶׁל שְׁנֵים עָשָׂר מָנֶה, וּבֵין הָעַרְבַּיִם הִנְדְּוִין שֶׁל שְׁמֹנֶה מֵאוֹת זוּז, דִּבְרֵי רַבִּי מֵאִיר
In the morning he would wear linen garments from the Egyptian city of Pelusium worth twelve maneh, 1,200 dinars or zuz. These garments were very expensive due to their high quality. And in the afternoon he wore linen garments from India, which were slightly less expensive, worth eight hundred zuz. (Sefaria translation and notation)
Eiruvin 56b - When measuring out the Shabbos limit you do so in a square measure.
As part of the stages of measure, it works out that;
נִמְצְאוּ תְּחוּמִין מִשְׂתַּכְּרִין שְׁמוֹנֶה מֵאוֹת אַמּוֹת לְכָאן וּשְׁמוֹנֶה מֵאוֹת לְכָאן
When one then squares the Shabbos boundaries, it is found that the Shabbos boundaries gain eight hundred cubits in this corner and eight hundred cubits in the opposite corner.
