A message segment is a block of encoded characters used to send text messages that exceed 160 characters. SMS messages are divided into segments when they are longer than this limit. Each segment is typically 160 characters when using standard GSM-7 encoding (the most common format for text messages). However, special characters, emojis, or non-standard encodings like UCS-2 may reduce the segment length to 70 characters per segment.
For example:
A 300-character message in GSM-7 encoding would be sent as 2 segments (160 + 140 characters).
A message with special characters that uses UCS-2 encoding may require 5 segments for 300 characters.
Since SMS carriers charge per segment, keeping messages concise can help control costs.