Every foreign learner will meet some words they do not know during the process when they study Chinese. If learners meet this condition when reading sentences, they can guess the meaning according to the contexts. Generally speaking, when the important words appear in reading material, you can usually find some words before or after them can explain the meanings. For example, if the foreign students never learned 素昧平生 when they study Chinese, it is difficult for them to understand. But the following context may appear 从没见过. So the sentence you have seen may probably 我和他素昧平生，从没见过.

Before or after the new words, there are usually some sentences can offer the clues to explain the contents. Therefore, when you learn in Chinese language courses, teachers often tell you to pay attention to understand the meaning according to the context. Usually, if the contexts provide the synonymous explanation, students who study Chinese often see the words like 即 and 就是 after the new words. We call them the signal words. For instance, 德律风就是电话.