In order to clearly answer your question, you’ll have to understand the following terminology:
MTU - Maximum transmission unit - this is the largest physical packet size measured in bytes that a network can transmit. Any packet larger than this MTU is divided or fragmented into smaller packets before transmission. The standard MTU on an Ethernet network is 1500 bytes plus the size of the L2 header and frame check sequence which is an additional 18 bytes. So standard MTU size for Ethernet is 1518.
Jumbo frame - A frame that is larger than the standard MTU size of 1518 bytes. This definition is vendor dependant and is not part of any IEEE standard. For Cisco, 1518 or 1522 in the case of Q in Q is the standard MTU. Anything larger is considered a jumbo frame.
When encapsulation from Layer 2 to Layer 3 occurs, if you have a frame that is say, 1600 bytes in size, in order for it to be encapsulated to layer 3, if there is an MTU setting of 1518, this frame will be fragmented into two parts, and each part will be placed in a separate packet. So one frame can be fragmented into two (or more) packets when encapsulated.
A network can be configured to accommodate jumbo frames, that is on layer 2, frames of sizes up to 9216 bytes for Gigabit Ethernet and faster interfaces can be used. 10/100Mbps ports are limited to 8092 bytes. MTU is configured on interfaces, such as physical interfaces of a switch or router, or on SVIs. Some platforms have a global MTU size configuration parameter. If all interfaces on all devices within a flat layer 2 network are configured to accommodate jumbo frames, this could be very useful especially when configuring the core or backbone of a network. Large bulks of data can be sent in this manner with much less overhead.
When using jumbo frames, it is important to be sure that the design you create is sound. If there is routing involved, that is if these large frames are going up to layer 3, then fragmentation of these frames may occur and this can easily slow down a network or even drop frames that cannot be fragmented.
I hope this has been helpful!