In the name of Allah, Most Compassionate, Most Merciful.
Some scholars have mentioned over 500 types of dhaeef hadith. However, all of these types can come under one of two main categories. These are the two main causes of weakness in a hadith.
1. Break in the chain of narration.
2. Weakness in the narrator.
The former is then divided into two sub-categories:

• Obvious break.
• Hidden break.

Under the first category, there are four types of hadith, namely:

1. المعلق Mu’allaq (Suspended)
2. المرسل Mursal (Loose)
3. المعضل Mu’dhal (Double Break)
4. المنقطع Munqate’ (Broken)

While there are two types of hadith under the second category, namely:

1. المدلس Mudallas (Misrepresented)
2. المرسل الخفي Mursal Khafi (Hidden Loose)

The latter is then divided into two sub-categories:

• Criticism concerning the narrator’s integrity.
• Weakness in his retention.

Under the first category, five causes of weakness are listed:

1. الكذب Kizb (Lie)
2. التهمة بالكذب Muttaham bil Kizb (Accusation of lying)
3. الفسق Fisq (Transgression)
4. البدعة Bid’ah (Innovation)
5. الجهالة Jahalah (Being unknown)

Similarly there are five factors that indicate to the weakness of a narrator’s retention:

1. فحش الغلط Fuhshul Ghalat (Huge blunder)
2. سوء الحفظ Soo-ul Hifz (Weak memory)
3. الغفلة Ghaflah (Heedlessness)
4. كثرة الغلط Kathratul Ghalat (Abundant mistakes)
5. مخالفة الثقات Mukhalafatus Thiqaat (Contradicting the reliable narrators)

Dhaeef is a term that can apply to any of the above types of weak hadith.