The terms "satchel" and "messenger bag" refer to different styles of bags, each with distinct features and historical uses. Here are the key differences:

1. **Design and Structure**:
- Typically has a rigid or semi-rigid structure.
- Often includes a flap that folds over the main compartment and is secured with buckles, snaps, or other closures.
- Generally rectangular in shape.

2. **Material**:
- Often made from leather, but can also be found in other materials like canvas or synthetic fabrics.

3. **Usage**:
- Traditionally used for carrying books and papers, making it popular among students and professionals.
- Can be used for casual or professional purposes.

4. **Carrying Style**:
- Usually features a long strap for shoulder or crossbody wear, and sometimes a handle for hand carrying.

Messenger Bag
1. **Design and Structure**:
- Typically softer and less structured than a satchel.
- Features a long strap designed to be worn across the body, with the bag resting on the lower back or hip.
- Often has a large flap that covers the main compartment, which may be secured with Velcro, buckles, or other fasteners.

2. **Material**:
- Commonly made from durable materials like canvas, nylon, or waterproof synthetics.
- Often includes reflective strips or other features for visibility.

3. **Usage**:
- Originally used by couriers, particularly bicycle messengers, hence the name.
- Designed for easy access while on the move, making it ideal for urban commuting and carrying items like laptops, documents, and personal belongings.

4. **Carrying Style**:
- Designed for crossbody wear, allowing for quick access without removing the bag.
- The strap is often adjustable and padded for comfort during extended use.

- **Satchel**: More structured, traditional, often made of leather, used for books and professional items.
- **Messenger Bag**: Less structured, designed for ease of access, made of durable materials, used for urban commuting and daily essentials.

These differences reflect their origins and typical use cases, though both can be versatile and fashionable choices depending on individual needs and preferences.