If I make a mistake, please correct me. A double consonant "sokuon" The Japanese word "tsu" (a small ”tsu” letter) is called a sokuon. 日本語の「っ」（小さいつ）は、促音と言います。 Sokuon means a sound like a something got stuck in your throat only for a moment, such as "yatta (did)", "gakko (school)", and "happy". 促音とは「やった」「がっこう」「ハッピー」など、小さな「っ」「ッ」で表される詰まる音のことで、一瞬のどが詰まるように聞こえる音です。 Let's think as rhythm, to explain that more simply. 分かりやすく音で例えましょう。 The sound of you clapping your hand only once is considered one clap. 1回だけ手を叩いた音を、一拍と考えます。 The "rabbito (rabbit)" as an example, you would clap your hands four times. 「ラビット」を例にしてみると、手を4回叩くことになります。 In other words, this sound has four pronunciations. つまり、この音は4つの音で発音します。 As another example, "bukku (book)" claps your hand three times. 他の例で「ブック」は、手を3回叩きます。 So this sound is pronounced three times. だから、この音は3回で発音します。 However, the pronunciation of the book is pronounced in one syllable in English. しかし英語では、「ブック」の発音を1シラブルで発音します。 That's the reason why it's hard to how to read small "tsu" sound. 小さい「っ」を読むのは難しいですね。