O furto é um crime.

O is the masculine singular definite article, equivalent to the in English.

In o furto, it literally means the theft, but in Portuguese, the definite article is often used to talk about something in a general sense. So O furto é um crime naturally means Theft is a crime.

This is very common in Portuguese:

• O açúcar faz mal em excesso. = Sugar is bad for you in excess.
• A honestidade é importante. = Honesty is important.

This is an important vocabulary point.

In Brazilian Portuguese legal usage:

• furto = theft, stealing something without direct confrontation or threat
• roubo = robbery, stealing something with violence, threat, or intimidation

So:

• If someone secretly steals a phone from a table, that is furto.
• If someone points a weapon at a person and takes the phone, that is roubo.

In everyday English, both may loosely be called stealing, but Portuguese often distinguishes them more clearly.

Portuguese has two main verbs for to be: ser and estar.

Here, é is from ser, which is used for:

• definitions
• classifications
• permanent or general characteristics

Since the sentence is defining/classifying furto as a crime, ser is the correct choice:

• O furto é um crime.

Using está would sound wrong here, because estar is usually used for temporary states, conditions, or location.

Um is the masculine singular indefinite article, equivalent to a or an in English.

So:

• um crime = a crime

The sentence is classifying theft as one member of the category crime:

• O furto é um crime. = Theft is a crime.

Portuguese often uses an article in this kind of classification sentence.

Compare:

• Ele é médico. = He is a doctor / He is a physician
• Isso é um problema. = That is a problem
• O furto é um crime. = Theft is a crime

In some cases Portuguese can omit the article, especially with professions after ser, but with a countable noun like crime, um is very natural and standard here.

Yes, furto is a masculine noun.

You can tell because it uses:

• o furto
• um furto

Many nouns ending in -o are masculine, though that is a pattern, not an absolute rule.

Because furto is masculine singular:

• definite article: o
• indefinite article: um

And crime is also masculine in Portuguese:

• o crime
• um crime

That may surprise English speakers, since English nouns do not have grammatical gender.

In Portuguese, grammatical gender does not always match the ending of the word.

Although many masculine nouns end in -o, some masculine nouns end in other letters or sounds, including -e:

• o crime
• o nome
• o leite

So crime is masculine even though it ends in -e. You simply learn it together with its article:

• o crime
• um crime

That is often the best habit for learners: memorize nouns with their article.

A simple approximate pronunciation for an English speaker is:

oo FOOR-too eh oong KREE-mee

A few notes:

• O is often pronounced like oo in Brazilian Portuguese.
• furto has the stress on the first syllable: FUR-to
• é sounds like eh
• um is nasal; it is not exactly like English oom. In connected speech, it can sound closer to ung or a nasal vowel.
• crime is usually pronounced roughly KREE-mee

If spoken naturally, the sentence may sound smoother and more connected than a word-by-word pronunciation.

Because this is a very straightforward statement with the normal Portuguese word order:

• O furto = subject
• é = verb
• um crime = predicate noun / complement

So the structure is basically: Subject + to be + noun

This is one reason the sentence feels easy for English speakers:

• Theft is a crime.
• O furto é um crime.

Yes, you may hear or see Furto é crime, especially in slogans, headlines, public notices, or emphatic statements.

Compare:

• O furto é um crime. = a full, standard sentence
• Furto é crime. = more compact, slogan-like, and very common in public messaging

Both are understandable, but the version with articles sounds more like a complete neutral sentence for study purposes.

Yes, it can.

Furto is a general term for theft, so it can include stealing from a store, depending on the context. In everyday speech, someone might also use more specific expressions such as:

• furto em loja
• shoplifting is sometimes described rather than translated with one single everyday word

But as a legal/general word, furto is broad and absolutely fits the idea of theft.

Yes. It is a very common structure used to define or classify things:

• A corrupção é um problema. = Corruption is a problem.
• A fraude é um crime. = Fraud is a crime.
• O respeito é uma virtude. = Respect is a virtue.

So O furto é um crime is a very natural model sentence for learning how Portuguese expresses definitions and general truths.