Mem

Mem is the 13th letter of the Alephbet, one that makes the 'm' sound (as in 'mess'):

Note from the character pictograph that Mem is 'open' when used in the mediall form. In this case, the character is again formed from a combination of a Vav (on the left) and Kaf.

However, Mem is the second letter of the Hebrew alphabet which has a sofit form for use at the end of the sentence. When this happens, the character has a closed form as seen in the following screenshot:

When used at the end of the sentence, you can see that the character is considerably more 'boxy' than it is otherwise.

Introduction to Reading Hebrew
The first basics
The Hebrew AlephBet
The Letters of the AlephBet
Aleph
Bet (Beyt)
Gimmel
Dalet
Hey
Vav
Zayin
Chet
Tet
Yod
Kaf
Lamed
Mem
Nun
Samekh
Ayin
Pey (Fey)
Tsade (Tsadik)
Qof
Resh
Shin
Tav
The Significance of the Alephbet
The Basics of Hebrew Verbs
The Hebrew Verb Subject
The Hebrew Verb Object
Hebrew Verb Tenses
Hebrew Verb Voices and Moods
Hebrew Verb Participles
The Infinite Verb Version
Hebrew Nouns
Hebrew Noun Constructs
Using Prefixes With Nouns
Hebrew Pronouns
Hebrew Plural Nouns
Hebrew Adjectives
Identifying Hebrew Questions
Adverbs, Prepositions and Conjunctions
Hebrew Reading Conclusion