Twitter is a free social networking service which is used by all the registered members which are broadcast short posts called tweets. Twitter members can broadcast tweets and follow other users tweets by using multiple platforms and devices. Twitter and replies to tweets can be sent by cell phone text message, desktop client or by posting at the official website called Twitter.com. The default settings for Twitter are in public mode and in the Facebook or LinkedIn's members need to approve social connections, anyone can follow anyone on public Twitter. To weave tweets into a conversation thread or connect them to a general topic, members can add hashtags to a keyword in their post. Twitter include hyperlinks which are limited to 140 characters according to Twitter's Short Message Service (SMS) delivery system. Because tweets can be delivered to followers in real time, they might seem like instant messages to the novice user.